Looks like `sudo yunohost app fetchlist -n name -u https://...` now
returns an error when there's already an apps list named `name`.

This cause the install script to fail when trying to add a list named
`labriqueinternet` on a Cube that already has one.

I'm not sure if this behavior is new to Yunohost 2.6, but I started
noticing the problem since 2.6.

This quick fix attempts to determine if a list named `name` already
exists by grepping on `name:` in the output of `listlists`. This is not
robust since it does rely on the output format of the command which
might change.