Use different extension for smali test files.

The test infra just searches for and opens all .jar files.
The different extension effectively hides the test files from it.

Bug: 147817558
Bug: 160391839
Test: m test-art-host-gtest
Change-Id: Ida3c102008b772841076df4e374532f7845b8c61
diff --git a/libartbase/base/common_art_test.cc b/libartbase/base/common_art_test.cc
index e327832..e0e44a8 100644
--- a/libartbase/base/common_art_test.cc
+++ b/libartbase/base/common_art_test.cc
@@ -488,7 +488,14 @@
   UniqueCPtr<char[]> executable_path(realpath(cmdline.c_str(), nullptr));
   CHECK(executable_path != nullptr);
   std::string executable_dir = dirname(executable_path.get());
-  return executable_dir + "/art-gtest-jars-" + name + ".jar";
+  for (auto ext : {".jar", ".dex"}) {
+    std::string path = executable_dir + "/art-gtest-jars-" + name + ext;
+    if (OS::FileExists(path.c_str())) {
+      return path;
+    }
+  }
+  LOG(FATAL) << "Test file " << name << " not found";
+  UNREACHABLE();
 }
 
 std::vector<std::unique_ptr<const DexFile>> CommonArtTestImpl::OpenDexFiles(const char* filename) {