Re-applied _override_sigchecks = True

After figuring out why this happened on a new
vm deployment it appears to be due to the gpg
check of epel causing problems that cause yyoom
to fail.

Fixes bug 1210657

Change-Id: I46f8972fb8676945a1c1edc6d1aba33c81faacce
Merge "Re-applied _override_sigchecks = True"