SCVMM - Power operations for VMs
Removed security vulnerability and added error logging

1) Security Vulnerability
Although unlikely, it is possible for the vm name to be tampered with and set to an executable command e.g. "rm -rf".
Instead of "white listing" or making sure the vm name conforms to Internet Standards (and RFC 1123), the GUID is now passed into the DOS power operation command instead of the name. This involves a simpler sanitizing approach - name.guid?

2) If a powershell operation returns an error it is now logged in the scvmm_log file.
Prepended MIQ() to log_header. Removed key? check
Merge pull request #22 from bronaghs/scvmm_powerops

SCVMM - Power operations for VMs