Fix docker apt install requirements

Add pkg-config dependency install for docker images. this is required
later on for mysql inside the container.

tools/docker/Dockerfile

@@ -30,6 +30,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     postgresql-client \
     sqlite3 \
     tzdata \
+    pkg-config \
     && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 
 RUN pip install wheel tox