Installs distro packages using bindep tool

Looks for a ``bindep.txt`` in a project's source directory, or failing
that a ``other-requirements.txt``. If one exists, run ``bindep`` on the
file to produce a list of required distro packages that do not exist and
then install the missing packages.

**Role Variables**

.. zuul:rolevar:: bindep_dir
   :default: {{ zuul.project.src_dir }}

   The directory to look for bindep files in.

.. zuul:rolevar:: bindep_profile
   :default: test

   A specific bindep profile to request.

.. zuul:rolevar:: bindep_file

   Path to a specific bindep file to read from.

.. zuul:rolevar:: bindep_command

   Path to the bindep command. Defaults to unset which will look for a
   system installed bindep. If bindep_command is not found, bindep
   will be installed into a temporary virtualenv.

.. zuul:rolevar:: bindep_fallback

   Path to a bindep fallback file to be used if no bindep file can be
   found in :zuul:rolevar:`bindep.bindep_dir`.