Change installer's subject SMACK label to System

Change installer's subject SMACK label to System

Both global and per-user pkg DB files have SMACK label as
System::Shared, which allows User labeled subjects to read, and System
labeled subjects to read/write.
To write pkg DB files, the SMACK label of the app installers is changed
to System.
Note that the global pkg DB files in /usr/dbspace/ are still protected
with DAC, as their owner is tizenglobalapp.

Change-Id: Ie193da8901a296e6489c4927ac4a0d3510b741f7
Signed-off-by: Youmin Ha <youmin.ha@samsung.com>