Default use of rapid_rsa_key

Default use of rapid_rsa_key

A secret and public key pair is available in the rapid directory:
rapid_rsa_key and rapid_rsa_key.pub. createrapid.py is now modified to
upload this key into OpenStack if the keypair does not already exist in
OpenStack. Which keypair to use is now only defined in
params_rapid.yaml. You can still define a key pair with a different name
in params_rapid.yaml. If the secret and public key files are not
available, a new keypair will be created and the secret key file will be
saved. The name of the secret key file is the name as the OpenStack
keypair name. The name of the public file is the same, with the pub
extension.

Change-Id: Ib8b5e4bf3a3d3138216698dc588a6908248220c0
Signed-off-by: Luc Provoost <luc.provoost@intel.com>