Validate CNAME alias doesn't allow forward slashes for forward zones

[mitruly]

We currently use the same validation regex for host names that we do for input names as we do CNAME data (including allowing of /). The issue is that only CNAMEs in reverse zones (e.g. zones in the form of x.x.x.in-addr.arpa. or x.x.x.x.ip6.arpa.) should be allowed to have /; forward slashes should not be allowed in forward zones.

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Good candidate files for changes:

• Update validations: BatchChangeValidations.scala and RecordSetValidations
• Add unit tests: BatchChangeValidationsSpec.scala
• Add end-to-end tests: create_batch_change_test.py

[pauljamescleary]

Thanks!!