ref: #1464
This tries to solve issues with races around process state. First it
adds the process mutex around the state call so that any state changes,
deletions, etc will be handled in order.
Second, for IsNoExist errors from the runtime, return a stopped state if
a process has been removed from the underlying OCI runtime but not from
the shim yet. This shouldn't happen with the lock from above but its
hare to verify this issue.
Third, handle shim disconnections and return an ErrNotFound.
Forth, don't abort returning all tasks if one task is unable to return
its state.
Signed-off-by: Michael Crosby <crosbymichael@gmail.com>
951c129bf1