Raise Error when pagination/groupby is missing

Raise NotImplementedError if db2 storage backend doesn't
support the pagination or the groupby API.

This change is needs by the blueprint db-tests-with-scenarios

Change-Id: I7dfeab96e30ae6640f969bb76da9a41045922a64
Move sqlachemy tests only in test_impl_sqlachemy

Some tests test the ceilometer storage model convertion to the
sqlachemy database model add must be in the test_impl_sqlachemy and not
in the base file.

This change is needs by the blueprint db-tests-with-scenarios

Change-Id: I057079fc27ef8b9a0a379f4d266d1fd3a8ce2671
Merge "Raise Error when pagination/groupby is missing"
Merge "Move sqlachemy tests only in test_impl_sqlachemy"