util/docker: Switch back to root user in jenkins-node

Leaving the user as coreboot caused the entrypoint to run as coreboot,
which means we couldn't mount directories or run sshd correctly.

Switching to root at the end of the file fixes this.

Signed-off-by: Martin Roth <gaumless@gmail.com>
Change-Id: Ie10e1d7ad4def0faafe3bcd580a77e23c3bfe948
Reviewed-on: https://review.coreboot.org/c/coreboot/+/79067
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

util/docker/coreboot-jenkins-node/Dockerfile

@@ -89,3 +89,4 @@ RUN echo 'export PATH=$PATH:/opt/xgcc/bin' >> /home/coreboot/.bashrc && \
 	echo "{{SSH_KEY}}" > /home/coreboot/.ssh/authorized_keys && \
 	chmod 0700 /home/coreboot/.ssh && \
 	chmod 0600 /home/coreboot/.ssh/authorized_keys
+USER root