Optimizations for import_logs.py

This set of patches addresses some optimizations in the log-analytics script.
Tests were made on an extract of 1 million lines from logs in ncsa format (dry-run).

Before the optimizations :
Total time: 219 seconds
Requests imported per second: 4554.54 requests per second

After :
Total time: 72 seconds
Requests imported per second: 13717.18 requests per second