[SIGMON-467] ack Zinurs feedback + [SIGMON-468] memory issue fixed

Context

• tasks: https://its.cern.ch/jira/browse/SIGMON-467, https://its.cern.ch/jira/browse/SIGMON-468

What was done

• spawn used to create child processes
• task moved outside the class (so self is not serialized and passed to the child processes)
• the ordering of the events is preserved

TODO

• ?

QA

• http://sonar/project/issues?branch=SIGMON-467_ack_zinurs_feedback&id=lhc-sm-qh&resolved=false
• no tests

Review objectives

• ? assessment of code functionality
• ? assessment of code quality
• ? identifying potential refactorings / logic common to other projects
• ? knowledge sharing
• ? getting help to understand a piece of code