docker/libtrust repository has been archived for several years now.
This commit replaces all the libtrust JWT machinery with go-jose/go-jose module.
Some of the code has been adopted from libtrust and adjusted for some of
the use cases covered by the token authorization flow especially in the
tests.
Signed-off-by: Milos Gajdos <milosthegajdos@gmail.com>
