Handle disappearing pids in mlock_report.py

If a pid disappears on us while we're reading, we should just continue
on.

EnvironmentError is just an alias for OSError since Python 3.3, so use
the latter name. [0]

[0] https://docs.python.org/3/library/exceptions.html#OSError

Change-Id: I3a25cca328e1469f72c84a118a9691c1c0258bc4
Closes-Bug: #1926434
1 file changed