Fixed arduino server sending notifications after deregister.

Fixed arduino server sending notifications after deregister.

This fixes IOT-627.
Arduino server continuted to send observe notifications even after
client deregisters. This happened because a bool variable tracking if
light was under observation was not set to false.

Change-Id: Ic1f00915632251a9be8772ca3cc4b71373dc3b18
Signed-off-by: Mandeep Shetty <mandeep.shetty@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/2011
Reviewed-by: Omkar Hegde <omkar.m.hegde@intel.com>
Reviewed-by: Joseph Morrow <joseph.l.morrow@intel.com>
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Erich Keane <erich.keane@intel.com>