Run CMK Inventory async: Temporary Fix.

Since CMK inventory calls back into supervisor, which blocks the
teardown indefinitely, move it to it's own delayed go routine.

This fix has the unfortunate side-effect that if checks hit in the
window when teardown has completed but inventory has not run, cmk
will alert.
Merge pull request #20 from ooyala/inventory_async

Run CMK Inventory async: Temporary Fix.