Move walreceiver walrep test to run on mirrorless cluster

The walreceiver test establishes a walrep connection to the master's
walsender. With the recent change to start standby master by default
on gpdemo cluster, the mock walreceiver will be unable to create a
connection to the walsender since max_wal_senders is hardcoded to
1. Moving this to run only on mirrorless cluster makes more sense
since the assumption is to have an available walrep connection.

src/test/walrep/Makefile

@@ -8,16 +8,11 @@ include $(top_builddir)/src/Makefile.global
 
 WITH_MIRRORS ?= true
 REGRESS = setup
-# WALREP_FIXME: 'walreceiver' test gets confused now that the QD node has a standby,
-# too, in the default demo cluster. I (= Heikki) think that we should remove the
-# 'walreceiver' test altogether. Tt doesn't seem very useful, now that we have
-# WAL replication working and exercising the walreceiver code anyway.
-#walreceiver
 
 # These two tests can only run without mirrors due to limit of 1
 # walsender-walreceiver connection only
 ifeq ($(WITH_MIRRORS), false)
-REGRESS += generate_ao_xlog generate_aoco_xlog replication_views_mirrorless
+REGRESS += walreceiver generate_ao_xlog generate_aoco_xlog replication_views_mirrorless
 else
 REGRESS += replication_views_mirrored missing_xlog
 endif