Temp Folder Security

[sevensolutions]

The temp folder is shared across all allocations. Maybe it would be a good idea to create special subfolders for each allocation (maybe even within the alloc dir) and only permit the own app.

Sidenote: When using the dump request of the management API it will also temporarily write the dumps to the temp directory which could be a security risk.

[sevensolutions]

Usefull hints: https://stackoverflow.com/questions/5437723/iis-apppoolidentity-and-file-system-write-access-permissions

Also related to: #17

[sevensolutions]

195926a fixes two things:

1. We've applied too much environment variables on the app pool. Some of them did belong to the nomad_iis process itself, not to the user's job.
2. I'am now overwriting the TMP and TEMP variables to use the alloc-dir's "tmp" folder, because it seems to be prepared for this usecase. See: https://developer.hashicorp.com/nomad/docs/concepts/filesystem