Bug/Time-machine exits before all the records have been comited to DB

[buixor]

Describe the bug
When processing logs in time-machine mode, crowdsec signals all the go-routines to exit once the acquisition is finished.
However, sometime, overflows might be still waiting to be pushed to DB (ie. bucket is still sending its overflow) and the shutdown mechanism doesn't check for this (it happens specifically if a very high % of your logs lead to an overflow being written to DB).

A better solution would be to monitor the number of "live" buckets before deciding if we can exit properly.

To Reproduce
Process a log with a high ratio of logs leading to overflow (ie. trigger scenario).
At the end of the run, not all the overflows are written to database.

Technical Information (please complete the following information):

• Version: 0.3.0-rc0

[buixor]

fixed in #148