Resolve "Add an option to the reply command to exclude uploading of G_event belonginig to a give pipeline"

Closes #27 (closed)

Since we need to replay events based on a specific pipeline, we are going to resolve to add a new functionality in meg that replays a single pipeline (and the possibility to specify a single search)

$ meg replay-events \
   -replay-only-pipeline gstlal -replay-only-search AllSky \
   --source production --target test \
   --original-search  \
   1391712000 1395168000 

DO TO:

• add a function replay_gevents() in mock-event-generator/reply.py
• add the command pipeline in mock-event-generator/reply.py

Note: in the class GEventCreator, the methods create(group,search,event_time,delay) require that in the replay, the new event_time,delay be such that a time of the invocation, say now and given the replay_offset, their values should be:

• delay = now - (gev["gpstime"] + gev["reporting_latency"] - replay_offset) and should be > 0
• `event_time = gev["gpstime"] + replay_offset