- Change rclone/fs interfaces to accept context.Context
- Update interface implementations to use context.Context
- Change top level usage to propagate context to lover level functions
Context propagation is needed for stopping transfers and passing other
request-scoped values.
Tests have been randomly failing with messages like
listen tcp 127.0.0.1:51778: bind: address already in use
Rework all the test servers so they choose a random free port on
startup and use that for the tests to avoid.