Typographical correction of Arista ML2 help

The Configuration Reference Guide on docs.openstack.org contains
configuration tables generated based on the help strings defined
in the Python code.

Typographical errors in the source for the Arista ML2 plugin,
particularly a lack of spaces between the start and end of
continuing lines, were resulting in errors in the guide.

Change-Id: I793274d9bf631db890af57f242b99de99db6f1f6
Merge "Typographical correction of Arista ML2 help"