Update clustering tests for Continuous Integration

Update clustering tests for Continuous Integration

This commit is a re-try of the following commit:
https://git.opendaylight.org/gerrit/#/c/22652/

The following changes were made:
    Change global variables to match those used in CI
    All ssh sign-ins now use certificates rather than passwords
    Remove Sleeps where possible.
    Move repeated variables into variables.py.
    Move repeated keywords into libraries.

Change-Id: I3c67c9fa5cbbfb1219f38cb9741481c28357185a
Signed-off-by: Phillip Shea <phillip.shea@hp.com>