Make password masking more extensible

[Ben Nemec]

Currently we have a number of hard-coded lists of things to mask. It's probably fine to leave those, but it would be nice to have an API to add more entries to them so every consumer of the library doesn't have to push their needed patterns into the library itself.

For example: https://review.openstack.org/#/c/142704/1/oslo/utils/strutils.py

[ChangBo Guo(gcb) (glongwave)]

This is the fix : https://review.openstack.org/#/c/245658/

[ChangBo Guo(gcb) (glongwave)]

From Doug:

"We've gone back and forth on this in the past, and for me it always comes down to wanting consistent behavior across projects. oslo.utils is shared space precisely because we want all projects to help maintain it. That includes adding new keys to be filtered out of messages. Adding them to the library means that all projects benefit from the list. Maintaining a separate list in each project means we all have to reproduce the same work, and we have inconsistent security-related behavior."