Build required modules from default

Some required modules from host tool (such as imgdiff) are bound to
required from releasetools_common, but unfortunately required modules
from python_library_host does not work (b/140144201). To make this work
we should mark dependency from each host tool.

Bug: 152258157
Test: Build succeeded without system image
Change-Id: Iedfda9b48d78687d8f622b818eeb93896d4f119d

tools/releasetools/Android.bp

@@ -237,6 +237,16 @@ python_defaults {
             embedded_launcher: false,
         },
     },
+    // TODO (b/140144201) Build imgdiff from releasetools_common
+    required: [
+        "aapt2",
+        "boot_signer",
+        "brotli",
+        "bsdiff",
+        "imgdiff",
+        "minigzip",
+        "mkbootfs",
+    ],
 }
 
 python_binary_host {