package_manager.py: sort output of OpkgPkgsList().list
Without explicit sorting, the output generated by OpkgPkgsList().list
follows the order of packages in /var/lib/opkg/status, which appears
to be "random". Add sorting to make OpkgPkgsList().list behaviour
consistent with that of RpmPkgsList().list.
Signed-off-by: Andre McCurdy <armccurdy@gmail.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>