Fix the brief/full snapshot dumpsys

Bug: 188272116

'dumpsys package snapshot' has a brief mode and a full mode.  The
sense of the flag is backwards in the dump routine.  This fixes the
flag.

Test: Manual test after booting.
 * 'dumpsys package snapshot' - verify full listing
 * 'dumpsys package snapshot --full' - verify full listing
 * 'dumpsys package snapshot --brief' - verify brief listing

Change-Id: I8495efc87cec60195a19d16a4aab66609a603389