Fix get_column_num problem in heat-keystone-setup

get_column_num function searches the second line of command output,
to get the field number for a specific field.

But output of 'keystone user-list' may have an extra line: 'WARNING:
Bypassing authentication using a token & endpoint ...'

This messes up the functionality of get_column_num function

Closes-bug: #1260556
Change-Id: I8c6e7f939466154c5e31e6f019e20fb855e15878
Merge "Fix get_column_num problem in heat-keystone-setup"