init_db: Fix not to print warning log about no source file

init_db: Fix not to print warning log about no source file

There might be no source files for the system info database. For
example, when creating hal.img, there might be no /etc/info.ini and
/etc/config/model-config.xml.
 - I/O warning : failed to load "/etc/config/model-config.xml":
       No such file or directory
 - iniparser: cannot open /etc/info.ini
To prevent printing warning log about no such files, check their
existance before parsing them.

In addition, fixed log when there is no given --release argument for
the system_info_update_db(). Previously, it just printed null buffer
after the 'and', making the entire message end with just 'and'.
 - Make system info db(/hal/etc/system_info_db) by
       /hal/etc/config/model-config.xml and
And it made the following line seem like continued message from the
trailing 'and'. So fixed not to print 'and' when there is no given
--release argument.

Change-Id: Ic7bce9b46f3578b40fb3b07f54d43a36df37cf2f
Signed-off-by: Youngjae Cho <y0.cho@samsung.com>