Renames old $devstack_dir to $TOP_DIR

This patch renames $devstack_dir which is no longer defined
to $TOP_DIR. Fixes problem where initialisation of ec2 images
for tempest testing was failing.

Change-Id: Ie0cd43209e58c903b1fe6cc528a4971896e6fab1
Cinder: update osapi_volume_extension default.

Updates the Cinder config file to use the new extension
loader location.

Change-Id: I515e16e00b54c69ae3c09e64841818eb4a9c8f73
Handle nested xtrace states

The lib/database abstraction includes the appropriate database file that also
contains the $XTRACE bits at entry and exit.  The nested XTRACE handling overwrote
the value from lib/database.  So...make the nested files use their own
XTRACE variables.

Change-Id: Ibdfc8d7d1e1457a9bc889b781ce176b417789ea1
Merge "Handle nested xtrace states"
Merge "Cinder: update osapi_volume_extension default."
Merge "Renames old $devstack_dir to $TOP_DIR"