Bump python-swiftclient version

https://review.openstack.org/#/c/69187/ introduced SSL certificate checking
in python-swiftclient (released as v2.0). This patch ensures that the version
of swiftclient used will verify SSL certificates correctly.

This patch also documents the `swift_store_auth_insecure` configuration
option for bypassing the cert verification

DocImpact
SecurityImpact

Change-Id: I20ddab5c3359071daf7505268c72331e4c786987
Merge "Bump python-swiftclient version"