Added sessions tests

Partly-Implements: blueprint murano-api-devstack-gates

Change-Id: I0c7c8d09c81a30ff01594a32ee6cf8794da298af
Add services tests

Partly-Implements: blueprint murano-api-devstack-gates

Change-Id: I88cb5f1602951a0948991f64c217075493e6eda0