ci: Remove the need for dumb-init

Newer versions of Docker have a `--init` argument which spawns an init process
in the container, which we should be able to use everywhere now.

Author: alexcrichton

src/ci/docker/arm-android/Dockerfile

@@ -3,9 +3,6 @@ FROM ubuntu:16.04
 COPY scripts/android-base-apt-get.sh /scripts/
 RUN sh /scripts/android-base-apt-get.sh
 
-COPY scripts/dumb-init.sh /scripts/
-RUN sh /scripts/dumb-init.sh
-
 COPY scripts/android-ndk.sh /scripts/
 RUN . /scripts/android-ndk.sh && \
     download_and_make_toolchain android-ndk-r13b-linux-x86_64.zip arm 9
@@ -38,4 +35,4 @@ COPY scripts/sccache.sh /scripts/
 RUN sh /scripts/sccache.sh
 
 COPY scripts/android-start-emulator.sh /scripts/
-ENTRYPOINT ["/usr/bin/dumb-init", "--", "/scripts/android-start-emulator.sh"]
+ENTRYPOINT ["/scripts/android-start-emulator.sh"]

src/ci/docker/armhf-gnu/Dockerfile

@@ -73,14 +73,9 @@ RUN arm-linux-gnueabihf-gcc addentropy.c -o rootfs/addentropy -static
 # TODO: What is this?!
 RUN curl -O http://ftp.nl.debian.org/debian/dists/jessie/main/installer-armhf/current/images/device-tree/vexpress-v2p-ca15-tc1.dtb
 
-COPY scripts/dumb-init.sh /scripts/
-RUN sh /scripts/dumb-init.sh
-
 COPY scripts/sccache.sh /scripts/
 RUN sh /scripts/sccache.sh
 
-ENTRYPOINT ["/usr/bin/dumb-init", "--"]
-
 ENV RUST_CONFIGURE_ARGS \
       --target=arm-unknown-linux-gnueabihf \
       --qemu-armhf-rootfs=/tmp/rootfs