Under some conditions, a VM can be created in labs with a mismatch between its "instance name" and its hostname; in those cases, our autosigner fails and puppet never runs.

Steps to reproduce:

1. Create an instance with an underscore in the name, i.e. "test_autosign"
2. since test_autosign.projectname.domain is not a valid hostname per RFC 1123, the hostname assigned to the VM will be test-autosign.projectname.domain
3. Autosign will fail on labspuppetmasters:

# /usr/local/sbin/validatelabsfqdn.py test-autosign.projectname.eqiad.wmflabs && echo OK
certname test-autosign.projectname.eqiad.wmflabs  is not for a real instance

# /usr/local/sbin/validatelabsfqdn.py test_autosign.projectname.eqiad.wmflabs && echo OK
OK

Solutions I see are either:

• Apply some heuristics when autosigning
• Return a clear error in horizon when someone tries to create an instance with an invalid hostname