When dropping privileges, check return values.
When dropping privileges, check return values.

setuid() and family can fail.  Check return values to make
sure this doesn't happen unexpectedly.

Also call setgid() to drop root group permissions.

Change-Id: Id06fbe6239e2ed2fe23368695e333514e0581e6d

xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base,xorware/android_frameworks_base