--allow-all-external is required for pip

At least one of the packages, argparse, is currently can't
be installed by simple 'pip install argparse==1.2.1'. To be
able to install it from external sources, --allow-all-external
option to pip can be used

Change-Id: Ib7199dca14b9bf471fb986b3ef4b805d22372a09
Closes-Bug: #1299678
Merge "--allow-all-external is required for pip"