Fixing security vuln by tightening race condition window.

A proper fix for this feature requires reworking binder permission
checking to take the selinux context and not the pid. This is feature
work that should be done for P to properly fix these race conditions
that occur elsewhere in the code.

Bug: 68217699
Test: KeyStore keygen permissions cannot be bypassed through PID cycling
Change-Id: I1ba5210010d6c413c9b1dbde3df0cc566400bfac
Merged-In: I1ba5210010d6c413c9b1dbde3df0cc566400bfac
(cherry picked from commit ef4f067c)