docker: Prepare builder to include flask and cherrypy

This is in preparation for the next commit.

contrib/Dockerfile.builder

@@ -51,4 +51,4 @@ RUN cd /tmp/ && \
     rm -rf bitcoin.tar.gz /tmp/bitcoin-$BITCOIN_VERSION
 
 RUN pip3 install --upgrade pip && \
-    python3 -m pip install python-bitcoinlib==0.7.0 pytest==3.0.5 setuptools==36.6.0 pytest-test-groups==1.0.3 flake8==3.5.0 pytest-rerunfailures==3.1 ephemeral-port-reserve==1.1.0 pytest-xdist==1.22.2 flaky==3.4.0
+    python3 -m pip install python-bitcoinlib==0.7.0 pytest==3.0.5 setuptools==36.6.0 pytest-test-groups==1.0.3 flake8==3.5.0 pytest-rerunfailures==3.1 ephemeral-port-reserve==1.1.0 pytest-xdist==1.22.2 flaky==3.4.0 CherryPy==17.3.0 Flask==1.0.2

contrib/Dockerfile.builder.i386

@@ -51,4 +51,4 @@ RUN cd /tmp/ && \
     rm -rf bitcoin.tar.gz /tmp/bitcoin-$BITCOIN_VERSION
 
 RUN pip3 install --upgrade pip && \
-    python3 -m pip install python-bitcoinlib==0.7.0 pytest==3.0.5 setuptools==36.6.0 pytest-test-groups==1.0.3 flake8==3.5.0 pytest-rerunfailures==3.1 ephemeral-port-reserve==1.1.0 pytest-xdist==1.22.2 flaky==3.4.0
+    python3 -m pip install python-bitcoinlib==0.7.0 pytest==3.0.5 setuptools==36.6.0 pytest-test-groups==1.0.3 flake8==3.5.0 pytest-rerunfailures==3.1 ephemeral-port-reserve==1.1.0 pytest-xdist==1.22.2 flaky==3.4.0 CherryPy==17.3.0 Flask==1.0.2