HUE-1452 [oozie] Support workflow credentials

Parameter values are inserted at submission time.
The correct XML is generated in the workflow and ihve action.

Hue reads the values through its local hive-site.xml:
_CNF_METASTORE_SASL = 'hive.metastore.sasl.enabled'
_CNF_METASTORE_URIS = 'hive.metastore.uris'
_CNF_METASTORE_KERBEROS_PRINCIPAL = 'hive.metastore.kerberos.principal'

The credential names are hardcoded for now:
<credential name='hive_credentials' type='hcat'>

Tests added for hive-site.xml parsing and XML workflow generation.