test: fix and split flaky join_vclock test

join_vclock test is assumed to verify that changes are not being lost
on the replica. Due to this the test is changed to explicitly check
that all changes on master are applied on replica.
Previously this test was also indirectly verifying that changes are
being applied in the correct order. Now there is separate test for
this, called replica_apply_order.
As far as changed join_vclock test might fail due to #4669, we are now
creating cluster out of fresh instances instead of using default
instance. Considering mentioned fixes it is not fragile anymore.

Closes #4160