Allow spaces in quoted SSH command arguments

The check_ssh_injection() method was rejecting arguments with spaces
even when they were quoted, this was causing problems with some volume
driver commands such as commands for a storage pool with spaces in the
name.

Closes-Bug: #1244415
Change-Id: Ie4b809e1b39fdb752cf634e6d3c0a3924d8ac52b
Merge "Allow spaces in quoted SSH command arguments"