Permit injecting content into /etc/hosts from heat

# Configuration

    hosts: '12.3.4 my-host.com'

Permit injecting content into /etc/hosts from heat

# Configuration

    hosts: '192.0.2.1 my-host.example.com'

Use rfc compliant example data in hosts element.
Use rfc compliant example data in hosts element.

Change-Id: I88d5d234ed4fd519de1841980254ce98b1c97a49
