[python][bugfix] Fix deadlock for outputs larger than buffer size

The wait command can deadlock when used with PIPE if the output is not read from the buffer. Therefore we have to call communicate see https://docs.python.org/3/library/subprocess.html#subprocess.Popen.wait

Communicate already waits until the process is finishes, no need for wait.

The bug was introduced in d3e69733

Fixes #305 (closed)