Fix gitblit duplicate definition

Commit I16181c1 added a monitor_service for gitblit with a title of
"gitblit". This, however, is also redefined by nrpe::monitor_service, as
defined in the gitblit::monitor class. Rename the latter to
"gitblit_process" to correctly reflect its contents and avoid the
duplicate definition.

Change-Id: Ied2dd42cbe6b31e91606a763550a6fcb6e86aa61