Fix intermittent test failure in TestStandardProcessScheduler

validateLongEnablingServiceCanStillBeDisabled on validateLongEnablingServiceCanStillBeDisabled(org.apache.nifi.controller.scheduling.TestStandardProcessScheduler)(org.apache.nifi.controller.scheduling.TestStandardProcessScheduler)  Time elapsed: 4.881 sec  <<< FAILURE!
java.lang.AssertionError: expected:<DISABLED> but was:<DISABLING>
  at org.junit.Assert.fail(Assert.java:88)
  at org.junit.Assert.failNotEquals(Assert.java:834)
  at org.junit.Assert.assertEquals(Assert.java:118)
  at org.junit.Assert.assertEquals(Assert.java:144)
  at org.apache.nifi.controller.scheduling.TestStandardProcessScheduler.validateLongEnablingServiceCanStillBeDisabled(TestStandardProcessScheduler.java:431)
. . .

validateLongEnablingServiceCanStillBeDisabled on validateLongEnablingServiceCanStillBeDisabled(org.apache.nifi.controller.scheduling.TestStandardProcessScheduler)(org.apache.nifi.controller.scheduling.TestStandardProcessScheduler)  Time elapsed: 2.071 sec  <<< FAILURE!
java.lang.AssertionError: expected:<1> but was:<0>
	at org.junit.Assert.fail(Assert.java:88)
	at org.junit.Assert.failNotEquals(Assert.java:834)
	at org.junit.Assert.assertEquals(Assert.java:645)
	at org.junit.Assert.assertEquals(Assert.java:631)
	at org.apache.nifi.controller.scheduling.TestStandardProcessScheduler.validateLongEnablingServiceCanStillBeDisabled(TestStandardProcessScheduler.java:421)
. . .