Additional changes necessary for Nimble deployment

This is a collection of changes that needs to be integrated for Nimble
SAN deployment. It is a reworking of the original code to handle various
aspects of doing this live. These include:

- update to ansible.cfg to point at our roles directory explicitly
- add forwarding agent capability to ursula
- a deploy-nimble-cinder playbook
- updates to sensu checks for nimble
- and ability to push private keys to a stack
Add ssh_private_keys default to common

Without an empty default the run will fail if ssh_private_keys is not
defined.
Merge pull request #512 from blueboxgroup/nimble3

Additional changes necessary for Nimble deployment
haproxy: Run as haproxy user, not nobody

Fix permissions on the TLS certificate and run the HAProxy service as
the haproxy user and group. This is a limited account created via the
haproxy package.

Explicitly define the PIDFILE to be used to override and default which
may change between the service script and haproxy.cfg.
arbiter: install percona-garbd package only
percona-arbiter: Fix on Trusty

- Split the percona-common tasks into separate precise and trusty yaml
files which are included based on the OS version.
- Add the version specific repo into the correct OS instead of the precise
repo on trusty.
- Leave the mysql-common package installed as python-mysqldb depends on
it which is needed by the Ansible MySQL modules.
Merge pull request #514 from blueboxgroup/haproxy-pid

haproxy: Run as haproxy user, not nobody
haproxy: Use PPA only, workaround service script

The PPA vbernat/haproxy-1.5 now provides packages for both precise and
trusty.
However, their latest release (1.5.5) included a bad service script
which fails to stop the service. This is due to start-stop-daemon taking
a pathto a pidfile and not an actual pid via command line options. The
packaged service script is incorrect, so we use our own for now.
rabbitmq: Fix config tests for cluster true/false
percona-common: Use ansible var for PPA version
haproxy: Correct mode on service script
rabbitmq: Disable cluster by default, fix tests
haproxy: Only restart_if_running
Merge pull request #515 from blueboxgroup/percona-garbd

percona, haproxy, ci: Fix pipeline testing