Cache sys.stdout instead of assuming it is equal to sys.__stdout__

[Nihlus]

When running under Mitogen, ipa_server and ipa_replica breaks execution by overwriting sys.stdout with sys.stdout.

With Mitogen, sys.stdout != sys.stdout at this point in the code, and changing it in this manner results in access to closed file descriptors for future invocations. Generally, it is recommended not to use sys.stdout and instead explicitly cache the current value of sys.stdout as proposed in this PR.

[Nihlus]

The issue has also been reported in Mitogen (mitogen-hq/mitogen#1214) since it is divergent behaviour against stock Ansible, but it's still something easily fixed in this module.