v2021pre → v2022dev1 forward port: Pin to a specific version of debos

Forward port of !148 (merged)

New debos needs newer fakemachine for the dynamic backends; However that will also mean a newer slirp-helper etc. So do a quick-fix now to pin it to the debos versions that has been in use for the past few months while ensure the new versions don't cause regressions

flatdeb-builder/Dockerfile

@@ -17,7 +17,8 @@ RUN apt-get update && \
         libostree-dev && \
     rm -rf /var/lib/apt/lists/*
 RUN go get -v -d github.com/go-debos/debos/cmd/debos
-RUN git -C ${GOPATH}/src/github.com/go-debos/fakemachine checkout wip/uml && \
+RUN git -C ${GOPATH}/src/github.com/go-debos/debos checkout -b uml d2ab9d3b08056c416bfbcd63c01199e14b2fc3b9 && \
+    git -C ${GOPATH}/src/github.com/go-debos/fakemachine checkout wip/uml && \
     go install github.com/go-debos/debos/cmd/debos
 
 # Build the slirp helpers, needed by UML for unprivileged networking