Add a RHEL6 post-prereq phase

Add some post-prereq actions for RHEL6:

 * 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