Archive: Add Add Lgetxattr and Lsetxattr implementations

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
archive: extract xattrs from tarfiles

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
archive: Detect file changes to capability bits

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
archive: Handle capabilities in tar files

If a file has a security.capability set, we push this to the tar file.
This is important to handle in e.g. layer files or when copying files
to containers, as some distros (e.g. Fedora) use capability bits as
a more finegrained version of setuid bits, and thus if the capabilites
are stripped (and setuid is not set) the binaries will fail to work.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)