vcsim: Update Dockerfile

The `vcsim` Dockerfile now uses `ENTRYPOINT` for the `vcsim` binary and
`CMD` for default listener address `0.0.0.0:8989`. A user can now easily
overwrite the default behavior without having to specify `/vcsim`
explicitly since it is the defined `ENTRYPOINT`.

Signed-off-by: Michael Gasch <mgasch@vmware.com>

Dockerfile.vcsim

@@ -43,4 +43,5 @@ EXPOSE 8989
 COPY vcsim /vcsim
 
 # Set entrypoint to application with container defaults
-CMD ["/vcsim", "-l", "0.0.0.0:8989"]
+ENTRYPOINT [ "/vcsim" ]
+CMD ["-l", "0.0.0.0:8989"]