rose suite-scan: fix call with argument

`rose suite-scan HOST` was broken.
Add test-battery.
Remove requirement for '@' in task hosts.
Fix typo.
Merge branch 'master' into fix-rose-suite-scan
Merge pull request #848 from arjclark/fix-ssh-user-bug

cylc.py: Remove requirement for '@' in task hosts.
Merge pull request #847 from matthewrmshin/fix-rose-suite-scan

rose suite-scan: fix call with argument