Fix CompatibilityBuildHelper to resupport partial paths.

A recent CL updated the CompatibilityBuildHelper's getTestFile
logic to search in more locations. This change fixes VTS as it
specifies partial subpaths as the file to retrieve.

Bug: 63625756
Test: run vts-codelab doesn't error out right away.
Change-Id: I2188917fc700eb879d8c271a60858d24e2f8a989
diff --git a/common/host-side/tradefed/src/com/android/compatibility/common/tradefed/build/CompatibilityBuildHelper.java b/common/host-side/tradefed/src/com/android/compatibility/common/tradefed/build/CompatibilityBuildHelper.java
index 750e79e..55b9604 100644
--- a/common/host-side/tradefed/src/com/android/compatibility/common/tradefed/build/CompatibilityBuildHelper.java
+++ b/common/host-side/tradefed/src/com/android/compatibility/common/tradefed/build/CompatibilityBuildHelper.java
@@ -267,6 +267,12 @@
 
         File testFile;
         for (String testDir: testDirs) {
+            testFile = new File(getTestsDir(), filename);
+            if (testFile.exists()) {
+                return testFile;
+            }
+            // The file may be in a subdirectory so do a more through search
+            // if it did not exist.
             testFile = FileUtil.findFile(new File(testDir), filename);
             if (testFile != null) {
                 return testFile;