[lldb][ARM] Misc improvements to TestEmulations

[DavidSpickett]

Summary

• Look for files that end width arm/thumb.dat, meaning we don't try to run, for example, vim swap files.
• Print the name of the test that failed.

lldb/test/API/arm/emulation/TestEmulations.py

 class ARMEmulationTestCase(TestBase):
 
     @no_debug_info_test
     def test_thumb_emulations(self):
         test_dir = os.path.join(self.getSourceDir(), "new-test-files")
         files = os.listdir(test_dir)
         thumb_files = list()
         for f in files:
-            if '-thumb.dat' in f:
+            if f.endswith('-thumb.dat'):
                 thumb_files.append(f)
 
         for f in thumb_files:
             test_file = os.path.join(test_dir, f)
             self.run_a_single_test(test_file)
 
     @no_debug_info_test
     def test_arm_emulations(self):
         test_dir = os.path.join(self.getSourceDir(), "new-test-files")
         files = os.listdir(test_dir)
         arm_files = list()
         for f in files:
-            if '-arm.dat' in f:
+            if f.endswith('-arm.dat'):
                 arm_files.append(f)
 
         for f in arm_files:
             test_file = os.path.join(test_dir, f)
             self.run_a_single_test(test_file)
 
     def run_a_single_test(self, filename):
         insn = lldb.SBInstruction()
         stream = lldb.SBStream()
         success = insn.TestEmulation(stream, filename)
         output = stream.GetData()
         if self.TraceOn():
             print('\nRunning test ' + os.path.basename(filename))
             print(output)
 
-        self.assertTrue(success, 'Emulation test failed.')
+        self.assertTrue(success, 'Emulation test {} failed.'.format(
+                        filename))