[Tizen] Drop privileges for extension process

This commit uses security-manager API to apply correct security context
for extension process.

Requires:
 - security-manager patch: https://review.tizen.org/gerrit/#/c/27977/
   (and dependent patches),
 - systemd patch: https://review.tizen.org/gerrit/#/c/27976/

[Verification]
  rpm -i security-manager-0.1.0-2.2.armv7l.rpm \
         libcynara-admin-0.2.2-10.1.armv7l.rpm \
         cynara-0.2.2-10.1.armv7l.rpm \
         libsecurity-manager-client-0.1.0-2.2.armv7l.rpm
  systemctl start cynara
  systemctl start security-manager
  systemctl enable security-manager
  (install and run app)