Preserve lowLevelHttpRequest, so that it's available to tests.

When lowLevelHttpRequest is not set via MockHttpTransport.Builder, buildRequest() creates a new instance of MockLowLevelHttpRequest. Due to what seems to be a bug, the newly created MLLHR wasn't saved to MHT instance. That means, getLowLevelHttpRequest() called on such instance returns null, making it impossible to inspect actual request being sent. For example, this bug made it impossible to verify headers of outbound HTTP requests.

This CL mirrors a change in the github repository: 8b59272

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=193200613

Author: pawelz

google-http-client/src/test/java/com/google/api/client/testing/http/MockHttpTransportTest.java

@@ -42,4 +42,3 @@ public void testBuildGetRequest_preservesLoLevelHttpRequest() throws Exception {
     assertThat(actualRequest.getHeaders().get("foo")).containsExactly("bar");
   }
 }
-