Fix port forwarding collisions in parallel run of multi-machine env

[legal90]

While doing a parallel run of multi-machine environment the race condition could happen:

...
There was an error while command execution. The command and stderr is shown below.

Command: ["/usr/local/bin/prlsrvctl", "net", "set", "Shared", "--nat-tcp-add", "winrm,2200,8977eda8-08ae-46d3-8923-469d8091ad69,5985", "--nat-tcp-add", "winrm-ssl,2201,8977eda8-08ae-46d3-8923-469d8091ad69,5986"]

Stderr: The rule with 'winrm' name already exists!

This PR fixes that by adding adds both class- and process-level locks, so port forwarding will be proceeded subsequently.

Also, I've improved the forward_ports helper by decreasing the number of driver method calls. Now it should work a little bit faster.

cc: @Gray-Wind @racktear @Kasen

[Gray-Wind]

👍