use real vagrant outside of gemset in shim

vagrant

#!/usr/bin/env bash
set -e
[ -n "$RBENV_DEBUG" ] && set -x

program="${0##*/}"
if [ "$program" = "ruby" ]; then
  for arg; do
    case "$arg" in
    -e* | -- ) break ;;
    */* )
      if [ -f "$arg" ]; then
        export RBENV_DIR="${arg%/*}"
        break
      fi
      ;;
    esac
  done
fi

# if vagrant is part of a gemset and we are not in any subfolder, use the standard vagrant
ruby_version="$(rbenv version)"
if [[ -z "$(rbenv gemset list | grep "${ruby_version%% *}")" ]]; then
  /opt/vagrant/bin/vagrant "$@"
else
  export RBENV_ROOT="/Users/gildas/.config/rbenv"
  exec "/usr/local/Cellar/rbenv/0.4.0/libexec/rbenv" exec "$program" "$@"
fi

Not perfect yet:

• Does not deal with same rbenv version but outside of the gemset.
• Uses hardcoded location for vagrant.
  That's a start shall we say.