Allow user to specify st2 repo branch to use.
Allow user to specify st2 repo branch to use.

pearsontechnology/st2contrib,pearsontechnology/st2contrib,pidah/st2contrib,armab/st2contrib,pidah/st2contrib,tonybaloney/st2contrib,armab/st2contrib,psychopenguin/st2contrib,psychopenguin/st2contrib,StackStorm/st2contrib,StackStorm/st2contrib,armab/st2contrib,pearsontechnology/st2contrib,tonybaloney/st2contrib,pidah/st2contrib,tonybaloney/st2contrib,pearsontechnology/st2contrib,StackStorm/st2contrib