Fix subprocess I/O descriptor leakage

[duynhaaa]

Because subprocess.Popen is used instead of subprocess.run, the stdout and stderr streams (bound to the subprocess.Popen through subprocess.PIPE) must be closed manually. Without doing so, the I/O descriptors held by them will not be released properly, causing the leakage.

Update: I encountered this problem while running a custom script for a long time (at least 3-4 days).

[savon-noir]

are you sure you pushed the right commit ? i don't see any fix for io descriptor in process.py

[duynhaaa]

are you sure you pushed the right commit ? i don't see any fix for io descriptor in process.py

You are right that I did push the wrong commit! Let me fix it real quick.

[duynhaaa]

I just pushed the correct commit this time. Please review and let me know if there's anything else that needs to be done.