PackageManagerService lock reduction: address comments

Bug: 161323622

Address three comments from previous commits:
 1. Change "computer(true)" to liveComputer() and "computer(false)"
    to "snapshotComputer()".  Delete the "// SNAPSHOT" comments as
    they are now unnecessary.
 2. Unit-test changes
 3. Four indentation errors that were introduced in ag/13027799.

Test: atest
 * FrameworksServicesTests:UserSystemPackageInstallerTest
 * FrameworksServicesTests:PackageManagerSettingsTests
 * FrameworksServicesTests:PackageManagerServiceTest
 * FrameworksServicesTests:AppsFilterTest
 * FrameworksServicesTests:PackageInstallerSessionTest
 * FrameworksServicesTests:ScanTests
 * FrameworksServicesTests:WatcherTest
 * UserLifecycleTests#startUser
 * UserLifecycleTests#stopUser
 * UserLifecycleTests#switchUser

Change-Id: I664666ce37f09c0ffa3ed15b8c24854f776668a4