Support multiple config file options on quantum-server command line

fix bug #1156831

Change-Id: Id05929c3114bc385c09fc25179cc15a358d38189
Add rhel to DISTRO match

Match RHEL and CentOS and provide them as a DISTRO prefix of "rhel"

Change-Id: Ida19130ce9499d4d1fd2360fadc6b870b24bbc95
Merge "Add rhel to DISTRO match"
Merge "Support multiple config file options on quantum-server command line"