fix symlink and dockerfile entrypoint (#221)

Fixes an issue where the dockerfile couldn't find the `storageos` binary

Dockerfile

@@ -8,6 +8,7 @@ RUN SEMANTIC_VERSION=$semantic_version make build
 
 RUN mkdir -p /root/.cache/storageos
 
-# The storageos binary must be in the PATH for the examples in the docs to work.
-RUN ln -s bin/storageos /usr/local/bin/storageos
-ENTRYPOINT ["/storageos"]
+# The storageos binary must be in the PATH for the examples in the docs to work,
+# as kubectl exec overrides the entrypoint
+RUN ln -s /go/src/github.com/storageos/go-cli/bin/storageos /usr/local/bin/storageos
+ENTRYPOINT ["storageos"]