add header for agency when authorized by aksk

[zengchen1024]

The api of Agency and Role need the header of "X-Auth-Token" that is a token with role of "Security Administrator". If using AKSK to authorize and invoke them, it needs another header of "X-Domain-Id".

[coveralls]

Pull Request Test Coverage Report for Build 315

• 5 of 17 (29.41%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.04%) to 68.811%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
openstack/identity/v3/roles/requests.go	5	9	55.56%
openstack/client.go	0	8	0.0%

Totals
Change from base Build 314:	-0.04%
Covered Lines:	11788
Relevant Lines:	17131

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💛 - Coveralls