Add tests for cinder/common/sqlalchemyutils.py

Add test cases:
- test_paginate_query_no_pagination_no_sort_dirs - tests
sorting only
- test_paginate_query_no_pagination - tests sorting only
- test_paginate_query_attribute_error
- test_paginate_query_assertion_error
- test_paginate_query_assertion_error_2
- test_paginate_query - tests both sorting and pagination
- test_paginate_query_value_error - is skipped now

Change-Id: Ibec636bf23872d221bac17f6514fc97bd09c4e86
Merge "Add tests for cinder/common/sqlalchemyutils.py"