LTTng based code profiling; focused on the path in ceph-osd for a write request to an object.

Added 13 tracepoints for ceph-osd daemon to provide timing analysis of functions in the path for primary and secondary write operations. These tracepoints collect timestamps within each of the instrumented functions and allow to track a complete transaction, i.e. the contributions to the overall latency for a write request.
A primary write starts when it arrives at the socket of ceph-osd and ends when the acknowledgement is sent back to the client.
At the layer of the Messenger, only the "simple" Messenger is instrumented; corresponding tracepoints for the "async" Messenger are pending.

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