[OPENENGSB-3502] Fixed checkstyle problems

Signed-off-by: Andreas Pieber <anpieber@gmail.com>
[OPENENGSB-3504] Fixed build on windows
ConnectorManagerImpl.connectorExists + tests added
ConnectorManagerImpl - small adjustments
ConnectorManagerImpl + tests - adjustments
ConnectorManagerImpl - minor change
Merge pull request #810 from lkavicky/OPENENGSB-3351/check-for-existing-connector

ConnectorManagerImpl.connectorExists + tests added