Add support for custom attributes for services

Automation can now use the "custom_keys", "custom_set", and "custom_get"
methods to manipulate the custom attributes on a service.  Any associated
custom attributes are now visible on the service details page.

https://bugzilla.redhat.com/show_bug.cgi?id=1108331
Fix specs broken by service model update

Service name is now a required field, which is breaking
several unit tests.

https://bugzilla.redhat.com/show_bug.cgi?id=1059834
Merge pull request #124 from dillaman/bz1059834-fix-specs

Fix specs broken by service model update
Merge pull request #13 from dillaman/bz1108331-service-custom-attributes

Add support for custom attributes for services