Add the ability to install/enable Heat plugins
Add the ability to install/enable Heat plugins

Adds the $ENABLE_HEAT_PLUGINS variable, which should be a list of
the names of the plugins the user wishes to install.

Change-Id: I2ba90002a8fad1cdce6543c89dc37c5912fe133e

nawawi/openstack,dirkmueller/devstack,dtroyer/devstack,openstack-dev/devstack,noironetworks/devstack,bswartz/devstack,dirkmueller/devstack,avvocatodemarchis/devstack,thomasem/devstack,samgoon/devstack,group-policy/devstack,mssumanth/devstack,prithivm/branch01,nawawi/openstack,varunarya10/devstack,Mahito/devstack,mssumanth/devstack,prithivm/branch01,group-policy/devstack,noironetworks/devstack,richliu/devstack,bigswitch/devstack,varunarya10/devstack,avvocatodemarchis/devstack,thomasem/devstack,dtroyer/devstack,openstack-dev/devstack,samgoon/devstack,bigswitch/devstack,bswartz/devstack,Mahito/devstack,richliu/devstack