python: fix packaging dependencies on minimal systems

python: fix packaging dependencies on minimal systems

If you install the top-level python package only on a minimal
system which has no other python packages installed then python
is not functional at all.  Without any extra packages installed
this error is seen:
  # python
  Traceback (most recent call last):
    File "/usr/lib/python2.7/site.py", line 64, in <module>
      import traceback
  ImportError: No module named traceback

Installing python-lang only partly fixes the problem as this
error still exists:
  # python
  Traceback (most recent call last):
    File "/usr/lib/python2.7/site.py", line 569, in <module>
      main()
    File "/usr/lib/python2.7/site.py", line 551, in main
      known_paths = addusersitepackages(known_paths)
    File "/usr/lib/python2.7/site.py", line 278, in addusersitepackages
      user_site = getusersitepackages()
    File "/usr/lib/python2.7/site.py", line 253, in getusersitepackages
      user_base = getuserbase() # this will also set USER_BASE
    File "/usr/lib/python2.7/site.py", line 243, in getuserbase
      USER_BASE = get_config_var('userbase')
    File "/usr/lib/python2.7/sysconfig.py", line 520, in get_config_var
      return get_config_vars().get(name)
    File "/usr/lib/python2.7/sysconfig.py", line 400, in get_config_vars
      import re
  ImportError: No module named re

(From OE-Core rev: c239564c768d0f305d8707103f4c59cf60431670)

Signed-off-by: Gary Thomas <gary@mlbassoc.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>