MB-100: missed RemMachShellCon.disconnect in installer

Change-Id: I939d7321298045a9cdee820d009abe2211722d31
Reviewed-on: http://review.couchbase.org/25223
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>