[FIX] runbot: remove useless pip warning

[d-fence]

When pip installs a package that contains a script, it goes in ~/.local/bin directory of the current user. This leads to a log warning to warn the user that the script won't be accessible by other users.

e.g.: WARNING: The script pygmentize is installed in '/home/odoo/.local/bin' which is not on PATH.

This is particularly annoying for documentation builds because it may confuse the users.

[AntoineVDV]

:+1:

[d-fence]

We may go for another solution that is to put the . local/bin in PATH instead. Because we don't want the wrong script to be called.