On *nix systems we might not have powershell installed and then finding
powershell.exe or pwsh.exe fails in some tests. If we instead mock
self.executable to return "powershell", then the tests pass and don't cause any
side effects.
Prior to this commit, the `Util::Powershell.execute_inline`
method didn't properly join the passed in command and instead attempted
to execute the array of strings. This commit updates that
behavior to join the command array prior to inserting it into the full
powershell command.
