Port osbuild/images v0.33.0 with dot-notation to composer

Update the osbuild/images to the version which introduces "dot notation"
for distro release versions.

 - Replace all uses of distroregistry by distrofactory.
 - Delete local version of reporegistry and use the one from the
   osbuild/images.
 - Weldr: unify `createWeldrAPI()` and `createWeldrAPI2()` into a single
   `createTestWeldrAPI()` function`.
 - store/fixture: rework fixtures to allow overriding the host distro
   name and host architecture name. A cleanup function to restore the
   host distro and arch names is always part of the fixture struct.
 - Delete `distro_mock` package, since it is no longer used.
 - Bump the required version of osbuild to 98, because the OSCAP
   customization is using the 'compress_results' stage option, which is
   not available in older versions of osbuild.

Signed-off-by: Tomáš Hozza <thozza@redhat.com>

vendor/github.com/gogo/protobuf/CONTRIBUTORS

@@ -0,0 +1,23 @@
+Anton Povarov <anton.povarov@gmail.com>
+Brian Goff <cpuguy83@gmail.com>
+Clayton Coleman <ccoleman@redhat.com>
+Denis Smirnov <denis.smirnov.91@gmail.com>
+DongYun Kang <ceram1000@gmail.com>
+Dwayne Schultz <dschultz@pivotal.io>
+Georg Apitz <gapitz@pivotal.io>
+Gustav Paul <gustav.paul@gmail.com>
+Johan Brandhorst <johan.brandhorst@gmail.com>
+John Shahid <jvshahid@gmail.com>
+John Tuley <john@tuley.org>
+Laurent <laurent@adyoulike.com>
+Patrick Lee <patrick@dropbox.com>
+Peter Edge <peter.edge@gmail.com>
+Roger Johansson <rogeralsing@gmail.com>
+Sam Nguyen <sam.nguyen@sendgrid.com>
+Sergio Arbeo <serabe@gmail.com>
+Stephen J Day <stephen.day@docker.com>
+Tamir Duberstein <tamird@gmail.com>
+Todd Eisenberger <teisenberger@dropbox.com>
+Tormod Erevik Lea <tormodlea@gmail.com>
+Vyacheslav Kim <kane@sendgrid.com>
+Walter Schulze <awalterschulze@gmail.com>