Modify RPM lists for RHEL6

Make various packages only install on Fedora distros; generally
letting pip install the missing dependencies on RHEL.

Change-Id: If497099d27aa9cd80e1c1cee1aff2ed6b076d309
Add RHEL6 post-prereq phase

Add some post-prereq actions:

 * pre-install dbus to avoid the service not having ever been started
 * a workaround for a hgtools/setuptools bug
 * install pycrypto and lxml as pip dependencies to ensure overrding
   of local versions
 * fix-up a dependency issue with prettytable by pre-installing

Change-Id: I089c07da32d211d25b14ce62cb61d2e3e8e6bb9f
Ensure polkit config is written for RHEL6 as well

Separate F18 polkit config and ensure it's written out for RHEL6, or
you get authentication errors with libvirt

Change-Id: Ib20fb0f4188e372fffe7736117ddbaf9c910195a
Grab upstream nodejs for RHEL6

RHEL6 has no nodejs in main packages or in EPEL.  The easiest way is
to just install the upstream binary version which works fine for the
very minimal usage by lesscss.

Change-Id: Ia35e7dbaf4c7add43797d6b7d0c846bab1cf0cb0
Skip pip mirrors for RHEL

The RHEL6 version of pip doesn't have support for mirrors, so skip
asking for them.

Change-Id: Iaf2900067bb4b41f88d8fe82ea16b6b53d6bcc60
Rename Qpid package for RHEL6

Qpid package name is different in RHEL6 to Fedora; also rewrite config
file to avoid authenication issues.

Change-Id: I29435ddaaf73ad0e060d2ee9a77a2f6d2e23bfdd
Add rhel6 as an allowed distro

Add RHEL6 as an allowed distro

Change-Id: I89fb68d18a0d2079493be93b230162679123881d