ActivityManager start-user has wait flag

Previously, when "am start-user" was called, the call would return
immediately, even though it might take some time to actually start the
user. This caused some CTS failures.

Here, we add an option for the call to wait until the user has been
started.

Note that 'started' here means UserState.RUNNING_UNLOCKED.
This uses UserController.startUser()'s IProgressListener argument to
wait for completion, but that currently waits until the user reaches
RUNNING_UNLOCKED. If the user has a lock, then unless it is unlocked,
the call will wait until it times out and will declare it failed,
even though the user has actually started (albeit is locked).

Bug: 126263999
Test: manual test of am start-user with and without -w
Change-Id: I6cb5d13cafda0f8708061923654106c504757564