c2a: Parse new cargo output

Cargo now outputs
'unittests src/lib.rs'
where before it output
'unittests'.

Bug: 246384761
Test: Add "test": true to argh_derive, regenerate, observe same bp file
Change-Id: Ieeab83761f5fe7cff88af1ce8293818736a6bb9b

scripts/cargo2android.py

@@ -1547,7 +1547,7 @@ class Runner(object):
     return ''
 
   def add_empty_test(self, name):
-    if name == 'unittests':
+    if name.startswith('unittests'):
       self.empty_unittests = True
     else:
       self.empty_tests.add(name)