Changed default value of "minimumRequiredDiskSpace" constant to "0". More in details

* From now on, each user defines his own minimum value of "minimumRequiredDiskSpace" per igniter. It's done to prevent annoing false alarms about missing disk space of read only volumes.
* Cleanup, minor igniter fixes, updates, improvements.

Signed-off-by: Daniel (dmilith) Dettlaff <dmilith@verknowsys.com>