[autotest] Split host acquisition and job scheduling.

This is phase one of two in the plan to split host acquisition out of the
scheduler's tick. The idea is to have the host scheduler use a job query
manager to query the database for new jobs without hosts and assign
hosts to them, while the main scheduler uses the same query managers to
look for hostless jobs.

Currently the main scheduler uses the class to acquire hosts inline,
like it always has, and will continue to do so till the
inline_host_acquisition feature flag is turned on via the shadow_config.

TEST=Ran the scheduler, suites, unittets.
BUG=chromium:344613
DEPLOY=Scheduler

Change-Id: I542e4d1e509c16cac7354810416ee18ac940a7cf
Reviewed-on: https://chromium-review.googlesource.com/199383
Reviewed-by: Prashanth B <beeps@chromium.org>
Commit-Queue: Prashanth B <beeps@chromium.org>
Tested-by: Prashanth B <beeps@chromium.org>
diff --git a/scheduler/rdb_lib.py b/scheduler/rdb_lib.py
index 73fc2ef..1449eaa 100644
--- a/scheduler/rdb_lib.py
+++ b/scheduler/rdb_lib.py
@@ -15,15 +15,16 @@
 # format more ameanable to the rdb/rdb request managers.
 class JobQueryManager(object):
     """A caching query manager for all job related information."""
-    def __init__(self, host_scheduler, queue_entries):
+    def __init__(self, queue_entries):
 
-        # TODO(beeps): Break the dependency on the host_scheduler,
+        # TODO(beeps): Break this dependency on the host_query_manager,
         # crbug.com/336934.
-        self.host_scheduler = host_scheduler
+        from autotest_lib.scheduler import query_managers
+        self.query_manager = query_managers.AFEHostQueryManager()
         jobs = [queue_entry.job_id for queue_entry in queue_entries]
-        self._job_acls = self.host_scheduler._get_job_acl_groups(jobs)
-        self._job_deps = self.host_scheduler._get_job_dependencies(jobs)
-        self._labels = self.host_scheduler._get_labels(self._job_deps)
+        self._job_acls = self.query_manager._get_job_acl_groups(jobs)
+        self._job_deps = self.query_manager._get_job_dependencies(jobs)
+        self._labels = self.query_manager._get_labels(self._job_deps)
 
 
     def get_job_info(self, queue_entry):
@@ -45,21 +46,19 @@
                 'priority': queue_entry.job.priority}
 
 
-def acquire_hosts(host_scheduler, queue_entries):
+def acquire_hosts(queue_entries):
     """Acquire hosts for the list of queue_entries.
 
     The act of acquisition involves leasing a host from the rdb.
 
     @param queue_entries: A list of queue_entries that need hosts.
-    @param host_scheduler: The host_scheduler object, needed to get job
-        information.
 
     @yield: An rdb_hosts.RDBClientHostWrapper for each host acquired on behalf
         of a queue_entry, or None if a host wasn't found.
 
     @raises RDBException: If something goes wrong making the request.
     """
-    job_query_manager = JobQueryManager(host_scheduler, queue_entries)
+    job_query_manager = JobQueryManager(queue_entries)
     request_manager = rdb_requests.BaseHostRequestManager(
             rdb_requests.AcquireHostRequest, rdb.rdb_host_request_dispatcher)
     for entry in queue_entries: