[lldb][ARM] Misc improvements to TestEmulations

* 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.

Reviewed By: clayborg

Differential Revision: https://reviews.llvm.org/D130467

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

@@ -20,7 +20,7 @@ def test_thumb_emulations(self):
         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:
@@ -33,7 +33,7 @@ def test_arm_emulations(self):
         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:
@@ -49,4 +49,5 @@ def run_a_single_test(self, filename):
             print('\nRunning test ' + os.path.basename(filename))
             print(output)
 
-        self.assertTrue(success, 'Emulation test failed.')
+        self.assertTrue(success, 'Emulation test {} failed.'.format(
+                        filename))