oslo.utils 2.6.0 causing tox test to hang

Forcing the change in requirements.txt is not feasible as all
entries there must match the global-requirements.txt file.
This forces a specific version of oslo.utils *before* the
requirements are loaded, thus ensuring that 2.6.0 is *not* used.

This should be considered a temporary fix only.

Change-Id: I4363c4b8b86efb15fd95d07ce6fff374024b3616
Partial-Bug: #1506402
Co-Authored-By: Amrith Kumar <amrith@tesora.com>

tox.ini

@@ -9,7 +9,8 @@ usedevelop = True
 install_command = pip install -U {opts} {packages}
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
-commands = {envpython} run_tests.py
+commands = pip install oslo.utils===2.5.0
+           {envpython} run_tests.py
            python setup.py testr --slowest
            {envpython} generate_examples.py
 whitelist_externals = bash