Move a method mock to setUp in an unit test

It makes more sense to mock the device serial in the setUp.

Test: presubmit
Change-Id: I1d48ae994c50bee8aaf15bba2162fda9782423fa
diff --git a/harness/src/test/java/com/android/csuite/core/AppCrawlTesterTest.java b/harness/src/test/java/com/android/csuite/core/AppCrawlTesterTest.java
index 53b22e0..22c6cc4 100644
--- a/harness/src/test/java/com/android/csuite/core/AppCrawlTesterTest.java
+++ b/harness/src/test/java/com/android/csuite/core/AppCrawlTesterTest.java
@@ -65,6 +65,7 @@
 
     @Before
     public void setUp() throws Exception {
+        Mockito.when(mDevice.getSerialNumber()).thenReturn("serial");
         mTestInfo = createTestInfo();
         mTestUtils = createTestUtils();
     }
@@ -384,7 +385,6 @@
 
     private AppCrawlTester createPreparedTestSubject(Path apkPath)
             throws IOException, ConfigurationException, TargetSetupError {
-        Mockito.when(mDevice.getSerialNumber()).thenReturn("serial");
         simulatePreparerWasExecutedSuccessfully();
         Mockito.when(mRunUtil.runTimedCmd(Mockito.anyLong(), ArgumentMatchers.<String>any()))
                 .thenReturn(createSuccessfulCommandResult());