Add a specialization of httpd conf for RHEL7/Apache 2.4's new auth directives

Also, make get-flavor.sh a bit more careful, and call 'rh' 'el6' to reflect
the fact that it's been used for both Centos and RHEL 6.x.  (rhel7 is still
named rhel7 simply because Centos 7 hasn't been validated.)

Signed-off-by: Dan Mick <dan.mick@inktank.com>