fix the leakage current ranges and warnings. GunHV stopper base on this attribute is postponed. Modify the message of write_not_allowed to the GnuLV.

git-svn-id: https://svn.code.sf.net/p/tango-ds/code/DeviceClasses/AcceleratorComponents/LinacAlba/trunk@18787 3b39871e-fe4b-0410-b5db-e82997f68959