plugins/driver: update driver interface to support streaming stats
client/tr: use streaming stats api
TODO:
* how to handle errors and closed channel during stats streaming
* prevent tight loop if Stats(ctx) returns an error
drivers: update drivers TaskStats RPC to handle streaming results
executor: better error handling in stats rpc
docker: better control and error handling of stats rpc
driver: allow stats to return a recoverable error
Update rawexec and rkt stop/kill tests with the patterns introduced in
7a49e9b68e519050a0c2ef0b67c33503bfbc51be. This implementation should be
more resilient to discrepancy between task stopping and task being marked as exited.
WaitForResult expects body to fail and retries few times before giving
up. Assertions inside the testfn body causes it to terminate abruptly
without retrying.
this allows us to drop a cyclical import, but is subobptimal as it
requires BaseDriver tests to move. This falls firmly into the realm of
being a hack. Alternatives welcome.
This PR plumbs the plugins done ctx through the base and driver plugin
clients (device already had it). Further, it adds generic handling of
gRPC stream errors.
