Added -u | --user option to cmd notification post

Examples:

$ adb shell cmd notification post --help| grep user
  -u|--user <user_id>

$ adb shell su shell /system/bin/cmd notification post --user cur marco polo
posting for user 10:
  Notification(channel=shell_cmd shortcut=null contentView=null vibrate=null sound=null defaults=0 flags=0 color=0x00000000 vis=PRIVATE)

$ adb shell su shell /system/bin/cmd notification post --user 42 marco polo
posting for user 10:
  Notification(channel=shell_cmd shortcut=null contentView=null vibrate=null sound=null defaults=0 flags=0 color=0x00000000 vis=PRIVATE)

$ adb shell su shell /system/bin/cmd notification post --user 10 ben 10
posting for user 10:
  Notification(channel=shell_cmd shortcut=null contentView=null vibrate=null sound=null defaults=0 flags=0 color=0x00000000 vis=PRIVATE)

Fix: 409408834
Test: see above
Flag: EXEMPT changes on debugging components only

Change-Id: I7ec2e6ce9a8b937a47cfc259672a92c6c59a24dd