golang: Don't require users to put \ into gowork.install

Previously it was required to put \ into multi-entry gowork.install, because the way it was processed was to directly pass it into bash command, and if \n were there the command was cut by bash and the trailing was considered as another command.

We can avoid that by explicitly processing \n in gowork.install and translate it to just ' '. This helps people because now gowork.install becomes just a regular multiline buildout entry, similar e.g. to gowork.cpkgpath et all.

Here is one example where it helps:

https://lab.nexedi.com/jerome/slapos/commit/95c45fe0#note_68408