add a simple pipeline unit test without mara db

[leo-schick]

Adds a simple unit test for a pipeline execution. To do so I changed the code that the 'mara' db is optional during the pipeline execution:

• node cost is not taken from the database
• RunLogger will skip logging events to the database when 'mara' database is not defined

[jankatins]

Would like to see a big warning printed when mara db is not there, but otherwise LGTM