Support AM API v3 credential arg
Support AM API v3 credential arg

Add support for v3 credential arg (list of dicts) with backward
compatibility for v2 credential arg (list of strings). Include filter
for geni credentials to avoid errors with non-geni credentials.

GENI-NSF/gram,GENI-NSF/gram,tcmitchell/geni-tools,plantigrade/geni-tools,ahelsing/geni-tools,GENI-NSF/gram,ahelsing/geni-tools,tcmitchell/geni-tools,plantigrade/geni-tools