Fix a typo in compute/manager::remove_volume_connection()

A typo made in the placement of a paren in a recent refactoring
resulted in definitely broken code. Unfortunately, this was not
in a tested path and so went unnoticed. This adds a test and fixes
the problem.

Change-Id: Id24169894ffda6da0301d1dc38b2f2bb29ebbd58
Merge "Fix a typo in compute/manager::remove_volume_connection()"