Sets the default KEY_PAIR_NAME for minion templates to be
what is defined in cloud.cfg. If cloud.cfg does not define
one then default to "jenkins-ssh".
Issue: RELENG-1066
Change-Id: I72bddf861174139048e1843a3631b3998ac32bef Signed-off-by: Thanh Ha <thanh.ha@linuxfoundation.org>