Minor changes to the opsdb schema; add a timestamp to record when the

DB was created, and a flag to indicate if the DB is transient (and
can be garbage collected).

sql/opsdb.sql

@@ -6,3 +6,7 @@ CREATE TABLE IF NOT EXISTS emulab_dbs (
   dbname varchar(64) NOT NULL default '',
   PRIMARY KEY  (dbname)
 ) TYPE=MyISAM;
+
+alter table emulab_dbs add date_created datetime default NULL;
+update emulab_dbs set date_created=now();
+alter table emulab_dbs add temporary tinyint(1) NOT NULL default '0';