Enable to get service types from configuration file

When services are registered to keystone without using default
service types, pollsters for the services don't work. This fix
enables the pollsters to get service types from ceilometer.conf.
If there is no entry in the file, the default service types
will be used.

Change-Id: Iab30b6e749f5d2af4ecb0bbf6fe1a137793f4c2c
Closes-Bug: 1353356
DocImpact: Add new parameters in ceilometer.conf
Merge "Enable to get service types from configuration file"