Make listener and connector fully asynchronous.

[hechaoli]

1. Return a Completable future instead of sync() on the bind() and connect() operations.
2. The interface of active connector is also changed. Now it returns a CompleteableFuture of OvsdbClient object.

Signed-off-by: Hechao Li hechaol@outlook.com

[coveralls]

Pull Request Test Coverage Report for Build 12

• 60 of 65 (92.31%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.3%) to 74.791%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
ovsdb-client/src/main/java/com/vmware/ovsdb/service/impl/OvsdbPassiveConnectionListenerImpl.java	28	33	84.85%
<!--	Total:	60	65	92.31%	-->

Totals
Change from base Build 11:	0.3%
Covered Lines:	1344
Relevant Lines:	1797

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💛 - Coveralls