Install rtslib when installing cinder

It doesnt make sense to put rtslib in tools/test-requires
since it is not directly using the python module while running
the tests, since the tests use cinder-rtstool.

Change-Id: Ib39b91e25f22b4943ef17eee50967828f7460b25
Signed-off-by: Chuck Short <chuck.short@canonical.com>
Merge "Install rtslib when installing cinder"