[Review] Request from 'tgoettlicher' @ 'SUSE/machinery/review_140805_'

Please review the following changes:
  * c70891a Show installation instructions for glance client on SLE12 if not installed
  * 6425d43 Merge branch 'fix-exception'
  * 5f42e71 Use correct exception
I think we should not add some more indirection here, that makes it too complicated for users. Having a command you can just copy and paste is a solution appreciated by lots of users.

To cover platform dependencies we should rather tailor the message to the system Machinery runs on, so that it always puts out the correct command. This is something we can gradually add, when we add support for more platforms, no need to over-abstract that now.