pythonPackages.keystoneclient: Disable tests

````
run_tests.sh: interpreter directive changed from "/bin/bash" to "/nix/store/nyj6xd7s1n1w8c0xdwk5ddhi7bjcyi9x-bash-4.3-p46/bin/bash"
No virtual environment found...create one? (Y/n) builder for ‘/nix/store/qcrhq2f7llvzyc37ili94ff50z7vlgn3-python2.7-keystoneclient-1.8.1.drv’ failed with exit code 1
error: build of ‘/nix/store/qcrhq2f7llvzyc37ili94ff50z7vlgn3-python2.7-keystoneclient-1.8.1.drv’ failed
````

pkgs/top-level/python-packages.nix

···
       sed -i 's@python@${python.interpreter}@' .testr.conf
     '';
 
-    doCheck = true;
+    doCheck = false; # The checkPhase below is broken
 
     checkPhase = ''
       patchShebangs run_tests.sh