Fix buiding containers doesn't complete

[hasebe]

Issues:

Building following containers doesn't complete as expected.

• photoalbum
• thumbnail
• safeimage

Status:

When running gcloud builds submit commands, those stuck with following outputs.

・・・
Running setup.py bdist_wheel for grpcio: started
  Running setup.py bdist_wheel for grpcio: still running...
  Running setup.py bdist_wheel for grpcio: still running...
・・・

Root cause:

It hits the issue here.

Solution:

Run pip install --upgrade pip before installing grpcio in Dockerfile.