Implement PATCH connection

[congwang09]

Resolves: https://github.com/atlanticwave-sdx/sdx-controller/issues/235

Implement PATCH endpoint. And replaced connection_id with service_id, for consistency.

[coveralls]

Pull Request Test Coverage Report for Build 10638427574

Details

• 22 of 45 (48.89%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.4%) to 57.762%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
sdx_controller/handlers/connection_handler.py	8	10	80.0%
sdx_controller/controllers/l2vpn_controller.py	14	35	40.0%
<!--	Total:	22	45	48.89%	-->

Totals
Change from base Build 10569856636:	-0.4%
Covered Lines:	1040
Relevant Lines:	1868

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💛 - Coveralls

[congwang09]

Note: patch -> delete then reprovisioning.

The new connection will be given a new service_id?

Yes, it'll have a new service_id, since we delete the old connection, and we keep the old connection in DB, just mark it as "deleted". There'll be conflict if we keep the same service_id.