CentOS/RH support for jenkins-sudo-grep.sh script.

* modules/jenkins/files/slave_scripts/jenkins-sudo-grep.sh: The log
file names and sudo error patterns are different in RHEL and CentOS
than in Debian and Ubuntu, so this leverages puppet's facter utility
to determine which OS family is in use and look in the correct place
for the correct error message.

Change-Id: Iaf3bbc60e408bac575d3724fb6181a5976c8004f
Reviewed-on: https://review.openstack.org/28649
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Khai Do <zaro0508@gmail.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins