Reset repository folder when call to "npm install" fails

[tidoust]

The Hook Machine clones Git repositories and run npm install. If that step fails, the script stops, but the repository folder is left as-is. The next time the machine performs a task on that repository, if no commit was made to that repo in the meantime, the machine will assume that everything is up and running in the repository folder.

It should rather drop the repository folder altogether or flag it somehow to have the machine attempt another npm install later on.