This prevents inconsistent errors when using a symlink, or when renaming
the binary;

Before this change;

    ln -s $(which docker) toto
    ./toto rune
    docker: 'rune' is not a docker command.

    ./toto run daslkjadslkjdaslkj
    Unable to find image 'adslkjadslakdsj:latest' locally
    ./toto: Error response from daemon: pull access denied for adslkjadslakdsj, repository does not exist or may require 'docker login': denied: requested access to the resource is denied.

After this change:

    ln -s $(which docker) toto
    ./toto rune
    docker: 'rune' is not a docker command.

    ./toto run daslkjadslkjdaslkj
    Unable to find image 'adslkjadslakdsj:latest' locally
    docker: Error response from daemon: pull access denied for adslkjadslakdsj, repository does not exist or may require 'docker login': denied: requested access to the resource is den>

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit a3af1f4)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>