[FAB-1857] Move orderer/mocks/configtx to common

https://jira.hyperledger.org/browse/FAB-1857



The configtx package was originally part of the orderer, so its mock was
created in the orderer.  However, configtx has moved to common and other
non-orderer packages may wish to utilize the mocks, so they should go to
common as well.

Change-Id: Ia94ffd80bf8f866aaeaaa5422a31db485f7e2a38
Signed-off-by: Jason Yellick <jyellick@us.ibm.com>