Lock our ansible version down to our own fork

This commit installs a version of ansible that we have curated with
specific commits.  Because ansible cannot be installed via a
requirements.txt file, a script was added to make this easier. As our
fork has the 'gather_facts: force' option, also enable this.
Add ansible 1.7.2-bbg to the requirements file

Thanks to @paulczar I am now adding our ansible fork to the
requirements file via tarball vs source. This is a much cleaner way
to go.
Fix broken CI run

./bin/install_ansible is no longer here
Set gather_facts on the plays that need it

Previously, I had set gather_facts on the common play only.  This
will work if one is running a full ansible run, but if you intend to
use tags, which target specific plays, then you need to set
gather_facts: force on each play that needs it.

The measure for which plays need it are those that make use of
hostvars[$host] type logic.  This commit will address those.