* src/security/security_apparmor.c: a few code cleanups following a
  review on the list

- Don't duplicate SystemError
- Use proper error code in domain_conf
- Fix a broken error call in qemu_conf
- Don't use VIR_ERR_ERROR in security driver (isn't a valid code in this case)

* configure.in: look for AppArmor and devel
* src/security/security_apparmor.[ch] src/security/security_driver.c
  src/Makefile.am: add and plug the new driver
* src/security/virt-aa-helper.c: new binary which is used exclusively by
  the AppArmor security driver to manipulate AppArmor.
* po/POTFILES.in: registers the new files
* tests/Makefile.am tests/secaatest.c tests/virt-aa-helper-test:
  tests for virt-aa-helper and the security driver, secaatest.c is
  identical to seclabeltest.c except it initializes the 'apparmor'
  driver instead of 'selinux'