Angelos Evripiotis authored Oct 22, 2018 and Phil Dawson committed Oct 23, 2018

Remove two uses of ExitStack that aren't necessary and make the code
a little harder to follow.

plugins/sources: refactor, rm needless ExitStack-s

See merge request !888

The REAPI allows a client to reconnect to an ongoing operation stream by
providing a WaitExecution(). If implemented on server side, BuildStream
will try to recover from connection errors using it.

#630