Remove default environment variable string
Remove default environment variable string

When this function returns a '' for a nonexistent environment variable,
kwargs.get() calls never fall back to their default, which
causes get_system_ca_file to always be ignored.

Change-Id: Ied68f1d63fdd204ea32f9144443b1d07d70528bf
Closes-Bug: 1512495

sapcc/python-monascaclient,stackforge/python-monascaclient,openstack/python-monascaclient,stackforge/python-monascaclient,openstack/python-monascaclient,sapcc/python-monascaclient,fzhaw/python-monascaclient,fzhaw/python-monascaclient