safer way to check for database existence

Signed-off-by: Steven Armstrong <steven@icarus.ethz.ch>

conf/type/__postgres_database/explorer/state

@@ -20,7 +20,7 @@
 
 name="$__object_id"
 
-if su - postgres -c "psql -l | grep -q '^ *$name'"; then
+if su - postgres -c "echo '\q' | psql '$name'" 2>/dev/null; then
    echo "present"
 else
    echo "absent"