MB-43478: Relax RR checks in the ReplicaEvictedBeforeActive test

The test is very sensible to minor differences of how much memory the
ItemPager frees up in different runs, which makes the test failing
sometimes.

But, the original purpose of the test is just ensuring that Replica VBs
are ejected before Active VBs, so just verify that.

Change-Id: Idedec7485e616392caf32663ec546397115cffbe
Reviewed-on: http://review.couchbase.org/c/kv_engine/+/143520
Tested-by: Build Bot <[email protected]>
Reviewed-by: Jim Walker <[email protected]>

Author: paolococchi

engines/ep/tests/module_tests/item_pager_test.cc

@@ -1017,12 +1017,10 @@ TEST_P(STItemPagerTest, ReplicaEvictedBeforeActive) {
         EXPECT_EQ(100, getRRPercent(*store->getVBucket(vbid)))
                 << vbid << " not fully resident after eviction";
     }
-    // Confirm the replica RR is "low"
-    // the replica RR could be constrained further, but checking
-    // it is below 20% to avoid making the test too sensitive to small
-    // changes in base memory usage.
+
+    // Confirm the replica RR is lower that active RR
     for (const auto vbid : replicaVBs) {
-        EXPECT_LT(getRRPercent(*store->getVBucket(vbid)), 20)
+        EXPECT_LT(getRRPercent(*store->getVBucket(vbid)), 100)
                 << vbid << " has residency higher than expected";
     }
 }