Allow for prettytable 0.7.x as well

Relax requirements to >= 0.6, < 0.8, as 0.7.x seems to
work as well. Added testcase to ensure this.

Change-Id: I1a1a709e6053451b1256a0d78f8fe8562fb10e62
Trapping KeyboardInterrupt sooner.

Currently a KeyboardInterrupt can be triggered by the user while the
client is communicating with keystone.  This patch moves the trap
higher up in the stack.

Fixes bug: 1157905

Change-Id: I16889c2d97bc4694ab27c863c62c27333e264b60
Merge "Allow for prettytable 0.7.x as well"