Update criu to 2.9

criu 2.8 and 2.9 contain various fixes,
so updating the version in the Dockerfile
to match the newer version.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Dockerfile

@@ -155,7 +155,7 @@ RUN git clone https://github.com/golang/lint.git /go/src/github.com/golang/lint
 	&& go install -v github.com/golang/lint/golint
 
 # Install CRIU for checkpoint/restore support
-ENV CRIU_VERSION 2.2
+ENV CRIU_VERSION 2.9
 RUN mkdir -p /usr/src/criu \
 	&& curl -sSL https://github.com/xemul/criu/archive/v${CRIU_VERSION}.tar.gz | tar -v -C /usr/src/criu/ -xz --strip-components=1 \
 	&& cd /usr/src/criu \