Fix missing of 'TB_LOG' in SConscript of ocserver

Fix missing of 'TB_LOG' in SConscript of ocserver

The defining of 'TB_LOG' is missing when building ocserver
for debug. It results in no serial output because log macro
functions like OC_LOG_INIT were redefined as nothing

Change-Id: I25881d16a2a7fefb17dd79c4349353c9befede77
Signed-off-by: Seung-woo Lee <sw0524.lee@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/324
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Caiwen Zhang <caiwen.zhang@intel.com>
Reviewed-by: Patrick Lankswert <patrick.lankswert@intel.com>