QE-361 support using a default host in tests

- create a default host
- support using the role as a valid host in calls to #on
  eg, on 'loadbalancer', "echo hello"
- create shell command to run on default host
- provide matchin commands to *_on
- spec tests for new commands, some backfill
review fixes and changes
Merge pull request #33 from anodelman/default-host-support

QE-361 support using a default host in tests