Race Condition when getting Ports for instances in TorPool

[jogli5er]

When populating TorPool with a larger number of TorProcesses, a race condition appears when getting the ports. This is a known problem of the get-port package (Compare sindresorhus/get-port#23), but as there is no better solution so far I suggest that we shift getting the default ports outside of the TorProcess into the creation function of the TorPool and protect the execution of the getPort function, such that no race conditions should appear.
A suggested fix can be found in pull request #14

[jogli5er]

As the pull request was merged, I'll close the issue