Allow pid file to be configurable

[renecannao]

Right now the path to pid file is hardcoded.
Should be configurable through config file only (no config db).

[negrusti]

On Ubuntu the pid file should go into /run instead of being written to persistent storage. This will ensure that the pid file is not present after reboot

[negrusti]

@renecannao - anything I can do to help with this? It is in the milestone for 1.4.0 but we are using 2.x?