CTS test for 'allowBackup' manifest attribute

Uses 2 apps that differ only by 'allowBackup' manifest attribute value.

Tests 2 scenarios:
1. App that has 'allowBackup=false' in the manifest shouldn't be backed
up.
2. App that doesn't have 'allowBackup' in the manifest (default is true)
should be backed up.

The flow of the tests is the following:
1. Install the app
2. Generate files in the app's data folder.
3. Run 'bmgr backupnow'. Depending on the manifest we expect either
'Success' or
'Backup is not allowed' in the output.
4. Uninstall/reinstall the app
5. Check whether the files were restored or not depending on the
manifest.

Test: cts-tradefed run cts-dev -m CtsBackupHostTestCases -t
android.cts.backup.AllowBackupHostSideTest

Bug: 38108587

Change-Id: I09d14e387193f3a0e5e3eb4561b1fc18c70b299a
8 files changed