This commit conditionally allows the os_keystone role to
install build and deploy within a venv. This is the new
default behavior of the role however the functionality
can be disabled.
Change-Id: Ie9e51926c96125a543e05eaa1912684fb01fecda
Implements: blueprint enable-venv-support-within-the-roles
Signed-off-by: Kevin Carter <kevin.carter@rackspace.com>