Get ApplicationInfo using self UID to make sure we have permission.

Otherwise the caller is checked for permission to get the
ApplicationInfo, and may be denied due to lack of INTERACT_ACROSS_USERS.

Bug: 142942524
Test: patched to internal master,
  1. Install TestDPC via adb
  2. Invoke "Set up Te..." from the launcher to create a work profile and follow "next" button and select "skip adding an account"
  3. Select TestDPC from the "work" tab of the list of all apps in launcher.
  4. Using built-in search look for "Password constraints" and tap it.
  5. tap "Minimum password length" and try to set it to 5.
  Before change: Neither user 1010193 nor current process has android.permission.INTERACT_ACROSS_USERS.
  After Change: password quality should be at least 131072 for setPasswordMinimumLength

Change-Id: I4018fac21c1ce40f4258be0dc39ebe0e8e1bd582