Ensure all file access is done with Sandbox::map()

"All" where it makes sence.
ut_rndssucli: run own (sandboxed) `ssud' instance

Otherwise existing (not-sandboxed) `ssud' instance is talked to and
system configuration is destroyed during test execution.
ut_urlresolver: Fix sanboxing of authorized_keys

Replace legacy code which does not use the Sandbox class.
Merge pull request #22 from martyone/fix-sandboxing

Fix sandboxing