Added --user option to 'dumpsys activity $ActivityName'.

Easier to debug on multi user environment.
Also make user option format consistent that "--user" should be
specified before sub command.

Bug: 218375003
Test: adb shell dumpsys activity --user cur test.app/.TestActivity
      adb shell dumpsys activity --user 0 top
Change-Id: Ie6f748bdc2218243c97273c09b8185f87e6b00cd