Wait for transfers to complete in replication2_pg:test_pg_proxy

Wait for transfers to complete in
replication2_pg:test_pg_proxy. Replication tests that test the n_val=1
request option can fail with insufficient_vnodes errors if the cluster
setup does not include waiting for transfers to complete. Change the
test_pg_proxy test case to wait until transfers complete on the "A"
and "B" clusters before proceeding.
Merge pull request #582 from basho/bugfix/replication2-nval1-request-failure

Wait for transfers to complete in replication2_pg:test_pg_proxy