Reinstate "Fix for Bug NMS-6551"

This reverts commit 55304f4105fe4ce64bcaf193fbf1c8064f3d1cbd.
It puts back the (currently broken) Alarmd patch for NMS-6551.
Add an extra NPE on AlarmPersisterImpl to make AlarmdTest and AlarmsPafeTest happy.
actually set the host properly
NMS-7195 fix rescan of nodes to update node label if labelSource=H,A
Make the 'Can't delete' message a debug, rather than warning.
be more graceful on an empty properties file
add some convenience methods to the entities for NMS-7231
fix weirdly-ordered log
allow logging a one-liner event summary at INFO

if you enable it in eventd-configuration.xml with logEventSummaries="true"
NMS-7231 rework handling of service deletion