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

Also fix some remaining inconsistencies in tox.ini

Change-Id: I2f690a9910351afd52703e4a0c537fa3b011f778
Closes-Bug: #1826823

README.rst

@@ -13,6 +13,6 @@ to use the REST API directly, CLI is provided only for convenience of users.
 
 * Free software: Apache license
 * Documentation: https://docs.openstack.org/osc-placement/latest/index.html
-* Source: https://git.openstack.org/cgit/openstack/osc-placement
+* Source: https://opendev.org/openstack/osc-placement
 * Bugs: https://bugs.launchpad.net/placement-osc-plugin
 * Release notes: https://docs.openstack.org/releasenotes/osc-placement/

tox.ini

@@ -18,7 +18,7 @@ setenv =
    PYTHONWARNINGS=ignore::DeprecationWarning:distutils,ignore::DeprecationWarning:site
    PYTHONDONTWRITEBYTECODE=1
 deps =
-   -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt}
+   -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
    -r{toxinidir}/test-requirements.txt
    -r{toxinidir}/requirements.txt
 commands = stestr run {posargs}
@@ -66,7 +66,9 @@ commands =
   coverage report
 
 [testenv:docs]
-deps = -r{toxinidir}/doc/requirements.txt
+deps =
+  -r{toxinidir}/doc/requirements.txt
+  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
 commands =
   rm -rf doc/build
   sphinx-build -W -b html -d doc/build/doctrees doc/source doc/build/html