Don't install tempest on stable kilo
Don't install tempest on stable kilo

Because of branchless tempest when we run tempest in a devstack env on
a stable branch we have to ensure it is venv isolated. The
INSTALL_TEMPEST flag should default to false on stable branches
accordingly so we don't try to install tempest globally.

Change-Id: Ic5faf357ead936793063845113686b33d85413c0

neerja28/Devstack_GlusterFS,neerja28/Devstack_GlusterFS