Chan.Part.API: join system channel using config block IT (hyperledger…

…#2082)

* Create system channel genesis block with configtx library

Use the configtx library to create the system channel genesis block,
as it provides an easy way in tests for explicit control over the
orderer endpoints and consenters for a channel.

FAB-18273

Signed-off-by: Will Lahti <[email protected]>

* Chan.Part.API: join system channel using config block IT

FAB-18273

Signed-off-by: Will Lahti <[email protected]>

* Chan.Part.API: Remove orderers, expectedBlockNum from IT helper

These were used previously but not any longer and should be removed.

Signed-off-by: Will Lahti <[email protected]>