Update pyparsing to 1.5.7

The version of cliff we are using depends on pyparsing>=1.5.7 but
python-quantumclient pulls 1.5.6 because it appears first in the
requirements processing.

The requirements change is in
    https://review.openstack.org/#/c/33406/

Fixes bug #1191866

Change-Id: Ib1c11b53813ff96b750f5ffe4997ad01907d32c3
Merge "Update pyparsing to 1.5.7"