use new openbsd-6.0 qcow2 image

ci/docker/x86_64-unknown-openbsd/Dockerfile

@@ -4,4 +4,4 @@ RUN apt-get update
 RUN apt-get install -y --no-install-recommends \
   gcc libc6-dev qemu qemu-kvm curl ca-certificates kmod cpu-checker
 ENV PATH=$PATH:/rust/bin \
-    QEMU=openbsd.qcow2
+    QEMU=2016-09-07/openbsd-6.0-without-pkgs.qcow2

ci/run-qemu.sh

@@ -19,10 +19,7 @@ export CARGO_TARGET_DIR=/tmp
 
 case $TARGET in
   *-openbsd)
-    pkg_add rust curl gcc-4.8.4p4
-    curl https://static.rust-lang.org/cargo-dist/2015-04-02/cargo-nightly-x86_64-unknown-openbsd.tar.gz | \
-      tar xzf - -C /tmp
-    export PATH=$PATH:/tmp/cargo-nightly-x86_64-unknown-openbsd/cargo/bin
+    pkg_add cargo gcc%4.9 rust
     export CC=egcc
     ;;