`fast-build` was performing a full Docker build minus the cli, and then
building cli locally. Separately, shasum was called with a `-p flag,
breaking some builds on Darwin.
Instead, rename `fast-build` to `build-cli-bin`, and restrict it to only
building the cli locally, without any Docker dependencies. Also modify
`bin/linkerd` to call `build-cli-bin` rather than
`docker-build-cli-bin`.
To perform an equivalent of `fast-build`:
`LINKERD_LOCAL_BUILD_CLI=1 bin/docker-build`
`shasum` fix cribbed from #2071.
Relates to #1704
Signed-off-by: Andrew Seigner <siggy@buoyant.io>
Andrew Seigner