Fix issue where loading the v6 schema overwrites all the custom validators

[hansmire]

This request is to fix issue 152. The problem is the custom format validators get overwritten when you create the referenced schemas and you are using version 6 of json schema. The fix adds the standard format validators to the reference schema if they don't exist already. It does not to overwrite the validators copied from the parent.

I hacked in a change to the IssueTest to allow me to add custom format validators. I think that the IssueTest probably needs to allow a SchemaBuilder to be passed in, but I did not want to make a proposal on how to do that. Let me know if there is a better way to add a custom format validator to IssueTest.

Also I made a change to always shut down the jetty service in IssueTest even if there is a failure.

[coveralls]

Coverage increased (+0.007%) to 91.477% when pulling 9f17850 on hansmire:issue152 into 6cb8ae4 on everit-org:master.

[erosb]

Hello @hansmire , thank you for submitting this PR.

Since there was a HUGE branch merged today into master, I didn't want to spend time on resolving conflicts, instead I copied most of your changes to the master branch.

So technically I close this PR, but I manually merged your changes, and included in the just now released version 1.8.0.