Update pip module to support Red Hat distros.

Adds a new pip::params module where we set parameters based on
the operating system.

Updates the pip::init module so that it makes use of distro specific
parameters.

Also, includes a change to pip::init so that a soft link is
created for /usr/bin/pip (pointing to /usr/bin/pip-python). This
is required in order for the Puppet pip provider to work on Red Hat
distributions. Seems like we should push a fix into Puppet for this
as well but having this live here for now seems reasonable.

Change-Id: Ifee6bc42fabcf65ee1241ffac38f3bead7335be1
Reviewed-on: https://review.openstack.org/18904
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins
Update openstack_project::base to support Red Hat.

Exclude apt specific resources from running on Red Hat distros.

Long term it would be nice to isolate apt specific changes into
a common module... but this seems reasonable for now.

Change-Id: Iab8f592d6b91eaf0c4f6346fe1d27b388119f880
Reviewed-on: https://review.openstack.org/18905
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins