Kill the real/isolated uid group, not the ApplicationInfo uid

This is a direct reimplementation in L of fixes applied to N in
these two commits:

8dc8d37c
e8741d23

Bug 19285814

Change-Id: I59bcc8f1d41c426e9da635bea9ad1d7c6756d5aa

Resolve merge conflict when cp'ing ag/941553 to mnc-mr1-release branch