[FIXED JENKINS-19248] Fix issue where a normal URL was set when registering some validators

This issue is affecting our Jenkins server.  It seems to only happen for some plugins, I think the publish over ssh plugin is an example.

I reckon Jenkins is the correct place to fix this as it seems to be safer to `try catch` the eval and continue if it fails.

Maybe it makes more sense to catch this further up the stack?  What do you think?