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
Raise ValueError if sort_dir is unknown

Raise ValueError in case of KeyError, when sort_dir is not
'asc' or 'desc'.

ValueError while adding pagination has never been raised before,
because if sort direction was incorrect, KeyError has been
raised while adding sorting.

Change-Id: Ia0366dbdf38557c4e6a9307fb27c77fd1c1873c3
Merge "Add tests for cinder/common/sqlalchemyutils.py"
Merge "Raise ValueError if sort_dir is unknown"