Simplify minion names

Summary:
Some minions contained only the hostname (e.g. "eglide").
Others were a FQDN (e.g. "dwellers.nasqueron.org").

This changes trim all minion to hostname without domain information.

This is coherent with pillar information and cd3273b0679a module.

Test Plan:
On Ysul, check if salt-call --local state.highstate test=True
tries well to parse paas-jail, webserver-legacy roles.

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1093