(FM-1913) fix passenger tests on EL derivatives

Previously we were excluding by "operatingsystem" == "RedHat" which
doesn't account for RedHat derivatives like Centos. This changes the
tests to check against "osfamily" instead.
Merge pull request #861 from justinstoller/bug/master/FM-1913-passenger-fails-on-el-7

(FM-1913) fix passenger tests on EL derivatives