Move constraints from install_command to deps

It's preferred not to have constraints in install_command as that
can cause problems with things like lower-constraints jobs which may
end up with conflicting constraints files. install_command is removed
entirely as it is no longer necessary.

Also updates the location of the constraints file to the releases
address as recommended by the release team.

Change-Id: I1415f66454d7394b6cadb5b0c9bb5b9666d10199

oslo.{{cookiecutter.module_name}}/tox.ini

@@ -5,10 +5,11 @@ skipsdist = True
 
 [testenv]
 usedevelop = True
-install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt} {opts} {packages}
 setenv =
    VIRTUAL_ENV={envdir}
-deps = -r{toxinidir}/test-requirements.txt
+deps =
+    -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+    -r{toxinidir}/test-requirements.txt
 commands = stestr run --slowest {posargs}
 
 [testenv:pep8]
@@ -30,7 +31,9 @@ commands =
 
 [testenv:docs]
 commands = sphinx-build -W -b html doc/source doc/build/html
-deps = -r{toxinidir}/doc/requirements.txt
+deps =
+    -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+    -r{toxinidir}/doc/requirements.txt
 
 [testenv:debug]
 commands = oslo_debug_helper {posargs}