Fix sandbox_rlimiter's logic for looking up its own filename.

[hodgestar]

The sandbox rlimiter needs to exec a Python instance that runs itself as a script to avoid importing parts of Twisted that get unhappy when closing filehandles. Currently the script does something like python __file__ but __file__ may be a .pyc file. This is ordinarily fine but if the .py file has just been updated the .pyc file will be invalid and this will fail.

This manifests as an error fro the sandbox that looks like:

[2013-10-21T08:03:08.550038, ERROR] /ve/bin/python: can't open file '/ve/src/vumi/vumi/application/sandbox_rlimiter.pyc': [Errno 2] No such file or directory

The fix is to replace the .pyc or .pyo with .py.

[hodgestar]

Any idea how to test this?

[coveralls]

Coverage remained the same when pulling 9a4655e on feature/issue-630-fix-rlimiter-exec-filename into 8f3bfa0 on develop.

[jerith]

Maybe set script_name at module level and have a test that does some import trickery to make sure foo.__file__ is a .pyc and foo.script_name is a .py?

[coveralls]

Coverage remained the same when pulling d4abe64 on feature/issue-630-fix-rlimiter-exec-filename into 8f3bfa0 on develop.

[jerith]

👍