Adds `ExasolPool`, makes log level configurable. #8

Job	Run time
distributed-tasks (lint:ci)	15s
distributed-tasks (test:dom)	27s
distributed-tasks (test:node)	23s
distributed-tasks (itest:dom)	2m 43s
distributed-tasks (itest:node)	2m 28s
Build and release	19s
	6m 35s

Provide feedback