In favor of keystone v2 support, SHOW_KEYSTONE_V2_RC now defaults
to False. SHOW_KEYSTONE_V2_RC setting is also deprecated.
Along with this change, "v3" part of "OpenStack RC File (Identity API v3)"
is now unnecessary, so "v3" information is dropped.
Change-Id: If0359e2dc1f2c8fb5f3c87046fd23043f94abc21