Change path of CNI build script and pin to a commit

As of containernetworking/cni commit 1b9caefba5670c59e0ccbf0b008d88da52a7d498,
the script to build has changed from 'build' to 'build.sh' which broke our
integration tests. Change the integration test Dockerfile to update this path,
and update the tutorial for good measure. Pin to current master to ensure this
breakage doesn't happen again.

Signed-off-by: Matthew Heon <mheon@redhat.com>

Dockerfile

@@ -56,11 +56,13 @@ RUN set -x \
 	&& rm -rf "$GOPATH"
 
 # Install CNI plugins
+ENV CNI_COMMIT d4bbce1865270cd2d2be558d6a23e63d314fe769
 RUN set -x \
        && export GOPATH="$(mktemp -d)" \
        && git clone https://github.com/containernetworking/cni.git "$GOPATH/src/github.com/containernetworking/cni" \
        && cd "$GOPATH/src/github.com/containernetworking/cni" \
-       && ./build \
+       && git checkout -q "$CNI_COMMIT" \
+       && ./build.sh \
        && mkdir -p /opt/cni/bin \
        && cp bin/* /opt/cni/bin/ \
        && rm -rf "$GOPATH"

tutorial.md

@@ -207,7 +207,7 @@ cd $GOPATH/src/github.com/containernetworking/cni
 Build the `cni` binaries:
 
 ```
-./build
+./build.sh
 ```
 
 Output: