superproject: Don't exit if superproject tag doesn't exist in manifest.

Don't exit if there are missing commit ids in superproject.

This change implements the following suggestion from delphij@:

"we should note the event (so we know that --use-superproject but there
 were some errors, e.g. manifest didn't specify commit id for some
 reason, or if there is no superproject but --use-superproject is
 used), print out a message telling the use that this is not support,
 but continue as if --no-use-superproject was specified?"

Changes:

superproject:
+ Added git_trace2_event_log as an argument to the constructor.
+ Sync method returns SyncResult a NamedTuple of
  ++ success - True if sync of superproject is successful, or False.
  ++ fatal - True if caller should exit, Or False.
+ UpdateProjectsRevisionId returns UpdateProjectsResult a NamedTuple of
   ++ manifest_path - path name of the overriding manifest file instead
      of None
   ++ fatal - True if caller should exit, Or False
+ _GetAllProjectsCommitIds returns CommitIdsResult a NamedTuple of
  ++ commit_ids - a dictionary with the projects/commit ids on success,
     otherwise None
  ++ fatal - True if caller should exit, Or False
+ Added  _SkipUpdatingProjectRevisionId a helper function to see if a
  project's revision id needs to be updated or not. This function is
  used to exclude projects from local manifest file.
+ Added the following error events into git_trace2_event_log
  ++ If superproject is missing in a manifest
  ++ If there are missing commit ids for projects.

command.py:
+ Deleted unused import - platform
+ Added git_trace2_event_log as a member so all subcmds can log error
  events.

main.py:
+ Initialized git_trace2_event_log as a member of command object.

init.py:
+ Deleted unused import - optparse

init.py:
+ Called sys.exit only if Sync returns exit=True

sync.py:
+ Called sys.exit only if Superproject's UpdateProjectsRevisionId returns
  exit=True
+ Reloaded the manifest only if manifest path is returned by
  UpdateProjectsRevisionId. If not, fall back to the old way of doing
  repo sync.

test_git_superproject:
+ Added code to verify error events are being logged.
+ Added a test for no superproject tag
+ Added test for UpdateProjectsRevisionId not updating the revision id
  with the commit ids.

Tested the code with the following commands.

+ Positive test case with aosp-master.
  $ repo_dev init -u persistent-https://android.git.corp.google.com/platform/manifest -b master --use-superproject
  NOTICE: --use-superproject is in beta; report any issues to the address described in `repo version`
  .../android/aosp/.repo/exp-superproject/925043f706ba64db713e9bf3b55987e2-superproject.git: Initial setup for superproject completed.

  Your identity is: Raman Tenneti <rtenneti@google.com>
  If you want to change this, please re-run 'repo init' with --config-name

  repo has been initialized in .../android/aosp

  $ repo_dev sync -j40 --use-superproject
  remote: Total 12 (delta 4), reused 12 (delta 4)
  NOTICE: --use-superproject is in beta; report any issues to the address described in `repo version`
  .../android/aosp/.repo/exp-superproject/925043f706ba64db713e9bf3b55987e2-superproject.git: Initial setup for superproject completed.
  ...
  repo sync has finished successfully.

+ Negative test case without superproject tag.
  $ repo_dev sync -j40 --use-superproject
  NOTICE: --use-superproject is in beta; report any issues to the address described in `repo version`
  repo error: superproject tag is not defined in manifest: .../android/aosp/.repo/manifest.xml
  error: Cannot get project commit ids from manifest
  error: Update of revsionId from superproject has failed. Please resync with --no-use-superproject option
  ...
  Checking out: 100% (1022/1022), done in 3.589s
  repo sync has finished successfully.

+ Test for missing commit_id for a project.
  $ repo_dev sync -j40 --use-superproject
  NOTICE: --use-superproject is in beta; report any issues to the address described in `repo version`
  .../android/aosp/.repo/exp-superproject/925043f706ba64db713e9bf3b55987e2-superproject.git: Initial setup for superproject completed.
  error: please file a bug using go/repo-bug to report missing commit_ids for: ['build/blueprint']
  error: Update of revsionId from superproject has failed. Please resync with --no-use-superproject option
  ...
  Checking out: 100% (1022/1022), done in 3.364s
  repo sync has finished successfully.

$ ./run_tests -v
  ...
  ...== 164 passed in 2.87s ==...

Bug: [google internal] b/189371541
Change-Id: I5ea49f87e8fa41be590fc0c914573e16c8cdfcfa
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/309162
Tested-by: Raman Tenneti <rtenneti@google.com>
Reviewed-by: Mike Frysinger <vapier@google.com>
diff --git a/main.py b/main.py
index 32ad0ff..f6631f5 100755
--- a/main.py
+++ b/main.py
@@ -208,7 +208,8 @@
           repodir=self.repodir,
           client=repo_client,
           manifest=repo_client.manifest,
-          gitc_manifest=gitc_manifest)
+          gitc_manifest=gitc_manifest,
+          git_event_log=git_trace2_event_log)
     except KeyError:
       print("repo: '%s' is not a repo command.  See 'repo help'." % name,
             file=sys.stderr)