Update Dockerfile.diagnostics to install core package.

Author: tillahoffmann

Dockerfile.diagnostics

@@ -2,6 +2,6 @@ ARG version=3.8
 FROM python:${version}
 
 WORKDIR /workspace
-COPY setup.py README.rst ./
-RUN pip install -e .
-COPY . .
+COPY core core
+RUN pip install --no-cache-dir -e core
+COPY diagnostics.py .