Misleading warning in srm scheme

[nataliaratnikova]

Motivation

The srm scheme currently requires space_token as extended_attribute, however when space_token is not set, rucio complains about extended_attributes and web_service_path not specfied.

Modification

Happens in these lines:

rucio/lib/rucio/core/rse.py

Lines 691 to 692 in 5fa4bb2

	if ('space_token' not in parameter['extended_attributes']) or ('web_service_path' not in parameter['extended_attributes']):
	raise exception.InvalidObject('Missing values! For SRM, extended_attributes and web_service_path must be specified')

Expected behavior

Ideally , space_token would be an optional attribute, and if not used, no spacetoken should be passed to FTS transfer job submission command. See also #574

[bbockelm]

Note - this is fixed in next but not in master. So, I think this becomes a backport exercise.