Use new connection string for constructor

This removes the classical 'bucket', 'host', 'port', etc. options in
favor of the new standardized connection string.

Change-Id: Ia98084f03834b27ab5033f427b18c2e48a6ccaf6
Don't try to destroy instance on async connection if non exists

Change-Id: Ic962fa0e913062b47fe9e9926df6eabe7949c029