Move manifest_fixer to a python_binary_host module

In preparation for making it use multiple files so that some
implementation can be shared with a new tool.

Also make manifest_fixer_test a python_test_host, and add it
to TEST_MAPPING.

Test: m checkbuild
Change-Id: Iaae177efcb978187b126d90359b82cdfd3176857

scripts/manifest_fixer_test.py

@@ -425,4 +425,4 @@ class AddExtractNativeLibsTest(unittest.TestCase):
 
 
 if __name__ == '__main__':
-  unittest.main()
+  unittest.main(verbosity=2)