enable multiple collector workers

currently, a single worker thread writes received samples into
database. this is fine for most occasions but during message
spikes, it is not enough. this patch increase amount of workers to
half the number of processors (so we can ensure ceilometer maintains
lightweight design)

this will also help validate mulitple worker setup works.

Partial-Bug: #1336755
Change-Id: I33037f2f9ebfda43238e5cd0cff75adbed65d055

Author: chungg

lib/ceilometer

@@ -154,6 +154,7 @@ function configure_ceilometer {
 
     if [ "$CEILOMETER_BACKEND" = 'mysql' ] || [ "$CEILOMETER_BACKEND" = 'postgresql' ] ; then
         iniset $CEILOMETER_CONF database connection `database_connection_url ceilometer`
+        iniset $CEILOMETER_CONF DEFAULT collector_workers $(( ($(nproc) + 1) / 2 ))
     else
         iniset $CEILOMETER_CONF database connection mongodb://localhost:27017/ceilometer
         configure_mongodb