Fix EL6 e2e test build failing on virtualenv permissions

[arm4b]

EL6 e2e test builds started failing with the following error

Running virtualenv with interpreter /opt/stackstorm/st2/bin/python2.7
Using real prefix '/usr/share/python/st2python'
New python executable in /tmp/st2tests/venv/bin/python2.7
Also creating executable in /tmp/st2tests/venv/bin/python
Overwriting /tmp/st2tests/venv/lib/python2.7/distutils/__init__.py with new content
Traceback (most recent call last):
  File "/usr/lib/python2.6/site-packages/virtualenv.py", line 2328, in <module>
    main()
  File "/usr/lib/python2.6/site-packages/virtualenv.py", line 713, in main
    symlink=options.symlink)
  File "/usr/lib/python2.6/site-packages/virtualenv.py", line 927, in create_environment
    install_distutils(home_dir)
  File "/usr/lib/python2.6/site-packages/virtualenv.py", line 1489, in install_distutils
    writefile(os.path.join(distutils_path, '__init__.py'), DISTUTILS_INIT)
  File "/usr/lib/python2.6/site-packages/virtualenv.py", line 373, in writefile
    with open(dest, 'wb') as f:
IOError: [Errno 13] Permission denied: '/tmp/st2tests/venv/lib/python2.7/distutils/__init__.py'

After looking closer, virtualenv setup which is executed by normal user creates symlinks to python2.7 libs. Because those files are owned by root, attempt to overwrite distutils/__init__.py fails with permissions error.

Add --always-copy flag to virtualenv which copies files rather then symlinking and makes more sense here.