clusters with many parameters are painful to create due to -P not being additive

[Robert Collins]

In TripleO we have very long command lines because we pass a mammoth string to heat stack-create. Being able to do
heat stack-create -f foo.yaml -P "Param=value" -P "Param2=value" would be the awesome.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/47922

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/47922
Committed: http://github.com/openstack/python-heatclient/commit/795d52c6418fa3beab2e3385da11ece8fca3db37
Submitter: Jenkins
Branch: master

commit 795d52c6418fa3beab2e3385da11ece8fca3db37
Author: Steve Baker <email address hidden>
Date: Mon Sep 23 17:55:55 2013 +1200

    Allow -P to be invoked multiple times

    If --parameters is specified more than once it is assumed
    that each one contains only one parameter key=value.

    This means semicolons are ignored if there is more than one -P
    specified.

    This should be fully backwared compatible, a single -P will
    be assumed to be semicolon delimited.

    Change-Id: Ic202ff3e0596b786cd5b07c53509f97a95d41585
    Closes-Bug: #1224825
    Closes-Bug: #1229030