Handle null string remote host.

The format returned by `cylc get-config` means that null strings may not
be handled correctly. This change should improve it some what.
Merge pull request #513 from matthewrmshin/remote-host-is-null-string

Handle null string remote host.
doc: fix versions.py reference
doc: fix wrong name
doc: fix directory ambiguity
Merge pull request #517 from benfitzpatrick/doc.feedback

rose documentation: implement more feedback and bug fixes