builder: print deprecation warning instead of failing for --stream
builder: print deprecation warning instead of failing for --stream

While performance will be worse, we can safely ignore the --stream
option when used, and print a deprecation warning instead of failing
the build.

With this patch:

    echo -e "FROM scratch\nLABEL foo=bar" | docker build --stream -
    DEPRECATED: The experimental --stream flag has been removed and the build context
                will be sent non-streaming. Enable BuildKit instead with DOCKER_BUILDKIT=1
                to stream build context, see https://docs.docker.com/go/buildkit/

    Sending build context to Docker daemon  2.048kB
    Step 1/2 : FROM scratch
     --->
    Step 2/2 : LABEL foo=bar
     ---> Running in 99e4021085b6
    Removing intermediate container 99e4021085b6
     ---> 1a7a41be241f
    Successfully built 1a7a41be241f

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

cpuguy83/cli,docker/cli,thaJeztah/cli,docker/cli,thaJeztah/cli,cpuguy83/cli