Revert "Add keystone v3 auth support"

This reverts commit a98c1f3617604c4871263ff9cc986b27f302ef46.
The new usage of session doesn't work with resources or events.

Conflicts:
	heatclient/tests/test_shell.py
Closes-Bug: #1349467

Change-Id: Ib5b0db81454abe647aca6461dd7bd5f197267fb8