When testing with "Client::Source::*::testChanges", two different
accounts must be used. Otherwise the two simulated SyncEvolution
clients share the same sync keys and testing fails.

The solution is to switch to a different account, derived by appending
_B to the original account ID, for the second client.

With this fix, the testing continues. But it also needs change in
client-test itself: "testChanges" had a check that all items can be
read, which is not the case for ActiveSync because there unmodified
item data is not available.