Adds tests to test domain slicing over complex coverages
Extends CTDPF test
Coverage Handler improvement to use newer API

Fixes the coverage handler for PyDAP to use the newer retrieval API in
the coverage model for retrieving the temporal parameter.
Merge pull request #1387 from lukecampbell/ctdpf-rebase

OOIION-1336 ERDDAP - updates the PyDAP Coverage Model Handler to use smarter retrieval API