Prior to this commit, the function used to determine the version of
Powershell would loop forever inside the Subprocess.execute function
because the process would never exit. This commit fixes that by passing
in a ruby block to capture the version from stdout instead of trying to
capture it from the returned process when it exits.
Adds powershell validation to ensure powershell is available on
the PATH and checks powershell version to ensure meets the
defined minimum powershell version.
