Skip tests in UsersV3TestJSON with an immutable user source 

Adds a skip_checks condition to UsersV3TestJSON to skip if immutable 
user source is true. resource_setup() in this class attempts to create
users, which will fail if the environment uses an LDAP directory for 
example.

Change-Id: I42c3b7a17bfb73079b1d05951636359324bed207
1 file changed