Close existing connection if one is open when connecting
Fixed setVolume and added setVolumeMuted call.

SetVolume was relying on an old way to set volume in castv2-client, see https://github.com/thibauts/node-castv2-client/commit/c01c7c40b01c02c8cfdff7bcb6443ef42ecb42de
Added device.close call to close the underlying castv2 connection
Updated test to include testing of new calls and fixed it up a bit
Added test for device re-use and re-connect