Revert "Exit when printing error about database config"

This reverts commit 2d7c346f0c8cefe622edc8fed47cc2782aeb9a9b.

Not setting DATABASE_TYPE is not a fatal error since it is
valid to create nodes which only run a subset of services,
and so a database may not be needed.

Change-Id: I7d957e628141ba333b6f38940b39845b18fba4df
diff --git a/stack.sh b/stack.sh
index 3f97919..c8905a7 100755
--- a/stack.sh
+++ b/stack.sh
@@ -584,7 +584,7 @@
 # The available database backends are listed in ``DATABASE_BACKENDS`` after
 # ``lib/database`` is sourced. ``mysql`` is the default.
 
-initialize_database_backends && echo "Using $DATABASE_TYPE database backend" || die $LINENO "No database enabled"
+initialize_database_backends && echo "Using $DATABASE_TYPE database backend" || echo "No database enabled"
 
 
 # Queue Configuration