FIX - if a coverage's set type doesn't exist in rasdaman, petascope should still start

[Bang Pham Huu]

Petascope should still start even if a coverage's set type doesn't exist in rasdaman. It should not show this coverage in GetCapabilities and should log in petascope.log, for example:

Set type 'test_mr_TO_BE_DELETED_Set' does not exist in rasdaman, but is required for coverage 'test_mr_TO_BE_DELETED'. Hint: create the missing set type, or delete the coverage in petascope with a DeleteCoverage request.