Ballista docker images fail to build

[andygrove]

Describe the bug
I ran ./dev/integration-tests.sh with latest from master just now and the docker build phase failed with:

Step 20/52 : RUN cargo chef cook $RELEASE_FLAG --recipe-path recipe.json
 ---> Running in 77d83a8813dd
error: failed to load manifest for workspace member `/tmp/ballista/ballista-examples`

Caused by:
  failed to read `/tmp/ballista/ballista-examples/Cargo.toml`

Caused by:
  No such file or directory (os error 2)
thread 'main' panicked at 'Exited with status code: 101', /usr/local/cargo/registry/src/github.aaakk.us.kg-1ecc6299db9ec823/cargo-chef-0.1.22/src/recipe.rs:142:27
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
The command '/bin/sh -c cargo chef cook $RELEASE_FLAG --recipe-path recipe.json' returned a non-zero code: 101

I probably broke this with the recent addition of the ballista-examples crate.

To Reproduce
Try and run the integration tests.