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
diff --git a/scripts/TEST_MAPPING b/scripts/TEST_MAPPING
new file mode 100644
index 0000000..cafecde
--- /dev/null
+++ b/scripts/TEST_MAPPING
@@ -0,0 +1,8 @@
+{
+  "presubmit" : [
+    {
+      "name": "manifest_fixer_test",
+      "host": true
+    }
+  ]
+}