Preserve /etc/sysconfig/docker across rpm update

Otherwise we have to reconfigure every time docker rpm got update.

Signed-off-by: WANG Chao <wcwxyz@gmail.com>

hack/make/.build-rpm/docker-engine.spec

@@ -169,7 +169,7 @@ install -p -m 644 contrib/syntax/nano/Dockerfile.nanorc $RPM_BUILD_ROOT/usr/shar
 /%{_unitdir}/docker.service
 /%{_unitdir}/docker.socket
 %else
-/etc/sysconfig/docker
+%config(noreplace,missingok) /etc/sysconfig/docker
 /%{_initddir}/docker
 %endif
 /usr/share/bash-completion/completions/docker