Allow setting CONF_DIR to move config files

**** Current error in Nova startup ****

Add configuration var CONF_DIR (default to '/etc') to allow
moving OpenStack project config files.  The common change
is to move them to $DEST:

CONF_DIR=${DEST}/etc

Also allows setting individual project _CONF_DIR in cases where
that was not possible before this change.

Change-Id: I920f541b57152293daa3cdf6dc12013be6b32b40
Merge branch 'set-conf-dir' into dt-test