nomad alloc exec options passing works incorrectly

With any container that has `ls`.
This works as expected:

`nomad alloc exec 6659bfac /bin/ls -l`

This prints _nomad help_ instead ls help:

`nomad alloc exec 6659bfac /bin/ls -h`

Expected behaviour: nomad should pass all options after container id to program.

Start by reproducing the issue with `nomad alloc exec 6659bfac /bin/ls -l` and `nomad alloc exec 6659bfac /bin/ls -h`, then trace the `alloc exec` argument parsing entry point. The fix is done when options after the allocation ID are passed to the container program, so `/bin/ls -h` shows ls help rather than Nomad help.

Written by the indexing model from the issue text.