Change the wrapper script from sh to bash

Because the directory create command uses Bash's handy syntax which
standard `sh` does not support.

Signed-off-by: kfei <kfei@kfei.net>
Add an explicit setting for root's $HOME

In some cases (probably older version of Docker), the home directory is
not correctly set such that rTorrent cannot find its rc file located in
`~/.rtorrent.rc`.

Thanks to @jingsta for reporting this issue.

Signed-off-by: kfei <kfei@kfei.net>