Intermittent failure in WskRuleTests with multiple controllers

While running the basic system test against an existing deployment having 2 controllers we are seeing intermittent failure in `Whisk rules should connect two triggers to two different actions, invoking them both eventually`.

```
Starting test Whisk rules should connect two triggers to two different actions, invoking them both eventually at 2018-09-14 10:41:39.039
check failed for activation 1b82a5b96be14c8a82a5b96be12c8a82: {"name":"t1to1b-1536921699040","subject":"guest","activationId":"1b82a5b96be14c8a82a5b96be12c8a82","publish":false,"annotations":[],"version":"0.0.1","response":{"result":{"payload":"got four words, period"},"success":true,"status":"success"},"logs":["{\"statusCode\":0,\"success\":true,\"activationId\":\"cab3196ee64140d5b3196ee64130d540\",\"rule\":\"guest/r2to2c\",\"action\":\"guest/a1to1a-1536921699040\"}"],"start":1536921701364,"namespace":"guest"}
Exception occurred during test execution: org.scalatest.exceptions.TestFailedException: List(RuleActivationResult(0,true,cab3196ee64140d5b3196ee64130d540,guest/a1to1a-1536921699040)) had size 1 instead of expected size 2
ERROR: deleting asset failed for r2to2d: org.scalatest.exceptions.TestFailedException: 404 was not equal to 200
```

And test failure trace is

```
org.scalatest.exceptions.TestFailedException: List(RuleActivationResult(0,true,cab3196ee64140d5b3196ee64130d540,guest/a1to1a-1536921699040)) had size 1 instead of expected size 2
at org.scalatest.MatchersHelper$.indicateFailure(MatchersHelper.scala:340)
at org.scalatest.Matchers$ResultOfHaveWordForExtent.size(Matchers.scala:2707)
at system.basic.WskRuleTests$$anonfun$9$$anonfun$apply$mcV$sp$9$$anonfun$apply$34$$anonfun$apply$35.apply(WskRuleTests.scala:353)
at system.basic.WskRuleTests$$anonfun$9$$anonfun$apply$mcV$sp$9$$anonfun$apply$34$$anonfun$apply$35.apply(WskRuleTests.scala:351)
at common.WskTestHelpers$$anonfun$withActivation$1.apply$mcV$sp(WskTestHelpers.scala:272)
at common.WskTestHelpers$class.withRethrowingPrint(WskTestHelpers.scala:304)
at system.basic.WskRuleTests.withRethrowingPrint(WskRuleTests.scala:34)
at common.WskTestHelpers$class.withActivation(WskTestHelpers.scala:271)
at system.basic.WskRuleTests.withActivation(WskRuleTests.scala:34)
at common.WskTestHelpers$class.withActivation(WskTestHelpers.scala:253)
at system.basic.WskRuleTests.withActivation(WskRuleTests.scala:34)
at system.basic.WskRuleTests$$anonfun$9$$anonfun$apply$mcV$sp$9$$anonfun$apply$34.apply(WskRuleTests.scala:351)
at system.basic.WskRuleTests$$anonfun$9$$anonfun$apply$mcV$sp$9$$anonfun$apply$34.apply(WskRuleTests.scala:349)
at scala.collection.immutable.List.foreach(List.scala:392)
at system.basic.WskRuleTests$$anonfun$9$$anonfun$apply$mcV$sp$9.apply(WskRuleTests.scala:349)
at system.basic.WskRuleTests$$anonfun$9$$anonfun$apply$mcV$sp$9.apply(WskRuleTests.scala:329)
at common.WskTestHelpers$class.withAssetCleaner(WskTestHelpers.scala:198)
```

Relates to #4003