consider/protect against malicious request overwrite

[xopham]

semgr8s has to store requests as files. it uses the admission request uid as file reference. this might be attacked by sending a high number of requests to intermittently overwrite the semgr8s request or results file and inject data into another request.

relevance and explotability of attack should be investigated. If feasible, it might be protected using a non-user provided, collision resistant file handler