Fix exception when api_extensions is set to empty
Fix exception when api_extensions is set to empty

test.is_extension_enabled() is not checking if
config_dict[service] list is empty

Added a check if config_dict[service] is empty the
function will return False which means no extensions
are enabled

Change-Id: I2ee64f205c393637b5fc65897f1489292781c0be
Closes-Bug: 1342516

mtreinish/tempest-lib,afaheem88/tempest-lib,JioCloud/tempest-lib,sorenh/tempest-lib,cneill/tempest-lib,varunarya10/tempest-lib