concurrent startup of multiple channels with shared transport is very slow, occasionally wedges.

Further to the testing in ChannelConcurrencyTest, we are now verifying 2.6.3-CR2 with the new shared transport enabled.

It appears to be a lot slower than the equivalent number of channels without shared transport, the CCT timeout of 2 minutes often being insufficient.

Will attach config and test cases.

I've not been able to catch it actually wedged yet, but will post as soon as I get a confirmed sighting.