common: work around overlay storage backend pip uninstall
common: work around overlay storage backend pip uninstall

Addresses:

  Collecting pip
  Downloading pip-9.0.1-py2.py3-none-any.whl (1.3MB)
Collecting wheel
  Downloading wheel-0.29.0-py2.py3-none-any.whl (66kB)
Installing collected packages: pip, wheel
  Found existing installation: pip 1.5.6
    Uninstalling pip-1.5.6:
Exception:
Traceback (most recent call last):
  File "/tmp/tmpqu31Wp/pip.zip/pip/basecommand.py", line 215, in main
    status = self.run(options, args)
  File "/tmp/tmpqu31Wp/pip.zip/pip/commands/install.py", line 342, in run
    prefix=options.prefix_path,
  File "/tmp/tmpqu31Wp/pip.zip/pip/req/req_set.py", line 778, in install
    requirement.uninstall(auto_confirm=True)
  File "/tmp/tmpqu31Wp/pip.zip/pip/req/req_install.py", line 754, in uninstall
    paths_to_remove.remove(auto_confirm)
  File "/tmp/tmpqu31Wp/pip.zip/pip/req/req_uninstall.py", line 115, in remove
    renames(path, new_path)
  File "/tmp/tmpqu31Wp/pip.zip/pip/utils/__init__.py", line 267, in renames
    shutil.move(old, new)
  File "/usr/lib/python2.7/shutil.py", line 300, in move
    rmtree(src)
  File "/usr/lib/python2.7/shutil.py", line 247, in rmtree
    rmtree(fullname, ignore_errors, onerror)
  File "/usr/lib/python2.7/shutil.py", line 256, in rmtree
    onerror(os.rmdir, path, sys.exc_info())
  File "/usr/lib/python2.7/shutil.py", line 254, in rmtree
    os.rmdir(path)
  OSError: [Errno 39] Directory not empty: '/usr/lib/python2.7/dist-packages/pip/backwardcompat'

when Docker is using the overlay fs backend. See:

  https://github.com/moby/moby/issues/12327

thewtex/cross-compilers,dockcross/dockcross,dockcross/dockcross,dockcross/dockcross,thewtex/cross-compilers,thewtex/cross-compilers,dockcross/dockcross,thewtex/cross-compilers