Sync process and str utils from oslo

This patch backports the necessary changes to fix both issues:
* Make execute method clean password in exception
* Make sure mask_password works properly

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The sync pulls in the following changes (newest to oldest):

63c99a0f - Mask passwords in exceptions and error messages
66142c34 - Make strutils.mask_password more secure
d6b55fb2 - Remove `processutils` dependency on `log`
cb5a804b - Move `mask_password` to strutils

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Backport in oslo-incubator: https://review.openstack.org/121365

Closes-Bug: 1343604
Closes-Bug: 1345233
SecurityImpact

Change-Id: I3b49b1d667f6ade9ae3f6765d735440a3e838917
Merge "Sync process and str utils from oslo" into stable/icehouse