Fix intermittent abort running Ekam in continuous

[vlovich]

ekam debug: ERROR: /ekam-provider/canonical/ekam/Driver.cpp:597: Tried to remove source file that wasn't ever added: edgeworker/tests/alarm.ew-test-bin.c++
terminate called after throwing an instance of 'ekam::OsError'
  what():  inotify_rm_watch(inotify): Invalid argument
make: *** [Makefile:360: continuous] Aborted (core dumped)

[vlovich]

Fixes #1

[kentonv]

This looks like it's turning a crash into an error log, but not actually fixing the state inconsistency that led to it? I wonder if it's a good idea to keep using a state that seems to have an inconsistency? Also if we're calling inotify_rm_watch() on an invalid watch descriptor, isn't there a risk that sometimes we call it on a valid descriptor that's the wrong descriptor, and accidentally stop watching a file?

[vlovich]

Open to suggestions. I was hoping logging the fd and wd would prove informative. Maybe just log them for now and propagate the failure?

[kentonv]

I don't think the fd is the problem. The first message, from Driver.cpp, indicates a higher level state inconsistency. The subsequent failure manipulating inotify is just a side-effect I think. Possibly a use-after-free even.