Unable to install Rally due to cmd2 dependencies on Python2

[Yusaku Sawai]

Trying to install from github repo. using pip the error occurs like following:

Collecting cmd2>=0.6.7 (from cliff>1.16.0->gnocchiclient>=3.3.1->rally==0.12.2.dev1)
  Using cached https://files.pythonhosted.org/packages/07/4a/f8c16175fa806b9c81f60688411b09a84a23decf774f2cdd5657e43dfe9b/cmd2-0.9.0.post1.tar.gz
cmd2 requires Python '>=3.4' but the running Python is 2.7.14

this has been caused by the EOL of cmd2 on Python2 with release of v0.9.0(https://github.com/python-cmd2/cmd2/releases/tag/0.9.0).

As an work around of this I added cmd2 version specification like following and installation has succeeded.
echo 'cmd2==0.8.7' >> requirements.txt.

This can be solved by fixing requirements.txt but, the other releases of Rally is also needed to be fixed.