SCVMM linux VMs have error message in their hostname

Linux VMs that do not have the Integration Services installed cannot communicate guest information back to the Hyper-v server.
The 'hostname' is one example of this, instead of displaying a blank value or a descriptive warning for the hostname, powershell displays the following ugly error:
 "getaddrinfo failed_x000A_ "
This PR addresses this by gracefully replacing this error message with the string "unavailable" as the hostname property value. I am open to enhancing this to "Integration Services not installed" or something along those lines.

https://bugzilla.redhat.com/show_bug.cgi?id=1138774
Merge pull request #572 from bronaghs/scvmm_linux_hostname_error

SCVMM linux VMs have error message in their hostname