GEODE-5652: use unlimited ThreadPoolExecutor in ExecutorServiceRule

[kirklund]

This changes the ExecutorServiceRule to use an unlimited ThreadPoolExecutor.

Improve or fixup a couple tests that use the ExecutorServiceRule:

• PartitionedRegionCreationDUnitTest
• DLockServiceLeakTest
• InterruptDiskJUnitTest (major overhaul)

This PR depends on PR #2405 (GEODE-5662: improve timeouts in ExecutorServiceRuleTest) which deleted two flaky tests from ExecutorServiceRuleTest because the tests were primarily testing ExecutorService instead of the rule itself.

[kirklund]

StressNewTest failed a couple times:

org.apache.geode.test.junit.rules.ExecutorServiceRuleTest > singleThreadedByDefault FAILED
    org.junit.ComparisonFailure: expected:<[1]> but was:<[2]>
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
        at org.apache.geode.test.junit.rules.ExecutorServiceRuleTest.singleThreadedByDefault(ExecutorServiceRuleTest.java:122)