fix: edit python generated pb2 import statements in general (#222)

In the previous version of `python/run-protoc.sh`, we selectively
edited import statements for `extensions_pb2`. With the prior addition
of `permissionmessages`, the package is broken. We need to edit those
as well.

In order to avoid this in the present and future, we generalize the
edits to all pb2 import statements in our generated code.

python/run-protoc.sh

@@ -46,7 +46,15 @@ do
     # `import extensions_pb2 as extensions__pb2` -> `from . import extensions_pb2 as extensions__pb2`
     for pb2_src in $src_path/*_pb2.py
     do
-        sed -i.old "s/^\(import extensions_pb2 as \)/from . \1/g"  $pb2_src
+        filename=$(basename "$pb2_src")
+
+        # cacheclient_pb2.py -> cacheclient_pb2
+        pb2_module_name=${filename%.py}
+
+        # Replace gRPC absolute imports with relative imports so the package
+        # will work when installed, eg:
+        # `import cacheclient_pb2` -> `from . import cacheclient_pb2`
+        sed -i.old "s/^\(import $pb2_module_name as \)/from . \1/g" $src_path/*_pb2.py
     done
 
     rm $src_path/*.old