Replace git.openstack.org URLs with opendev.org URLs

Thorough replacement of git.openstack.org URLs with their opendev.org counterparts.

Change-Id: I90c0338f37fb6c8ed3b555b2d9d6b76aff6dad76
Closes-Bug: #1825935

README.rst

@@ -24,6 +24,6 @@ such as encoding, exception handling, string manipulation, and time handling.
 
 * Free software: Apache license
 * Documentation: https://docs.openstack.org/oslo.utils/latest/
-* Source: https://git.openstack.org/cgit/openstack/oslo.utils
+* Source: https://opendev.org/openstack/oslo.utils
 * Bugs: https://bugs.launchpad.net/oslo.utils
 * Release notes: https://docs.openstack.org/releasenotes/oslo.utils/

tox.ini

@@ -5,7 +5,7 @@ envlist = py35,py27,pep8
 [testenv]
 install_command = pip install {opts} {packages}
 deps =
-  -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt}
+  -c{env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/master/upper-constraints.txt}
   -r{toxinidir}/test-requirements.txt
   -r{toxinidir}/requirements.txt
 commands = stestr run --slowest {posargs}