Change behavior of trust anchor

Change behavior of trust anchor

- Trust anchor certificate dir has fixed so it will not defined at manifest.
- Remove get/set codes about certificate directory.
- Enable trust-anchor on hybrid package.
  Please note that if both tpk and wgt package have trust-anchor node,
  wgt's setting will be appliced.

Related changes:
[pkgmgr-info] : https://review.tizen.org/gerrit/149784
[app-installers] : https://review.tizen.org/gerrit/149836
[tpk-manifest-handlers] : https://review.tizen.org/gerrit/150060
[wgt-manifest-handlers] : https://review.tizen.org/gerrit/150136

Change-Id: Ie110eb1b52695c985495f03b834c9bfd9e5bf960
Signed-off-by: Junghyun Yeon <jungh.yeon@samsung.com>