Use precise version for hbmpc-deps image

Dockerfile

@@ -1,8 +1,10 @@
-FROM sbellem/honeybadgermpc-deps AS build-compute-power-sums
+ARG HBMPC_DEPS_TAG="python3.7-slim-buster"
+
+FROM sbellem/honeybadgermpc-deps:$HBMPC_DEPS_TAG AS build-compute-power-sums
 COPY apps/asynchromix/cpp/ /usr/src/apps/asynchromix/cpp/
 RUN make -C /usr/src/apps/asynchromix/cpp
 
-FROM sbellem/honeybadgermpc-deps AS pre-tests
+FROM sbellem/honeybadgermpc-deps:$HBMPC_DEPS_TAG AS pre-tests
 
 COPY pairing /usr/src/pairing
 RUN pip install -v /usr/src/pairing/
@@ -27,6 +29,7 @@ FROM tests as pre-dev
 WORKDIR /
 
 # Install solidity
+# TODO look at https://github.com/ethereum/solidity/blob/e383b2bbbaeae33bd44d1e3b641ca922cf030c8d/.circleci/docker/Dockerfile.ubuntu1904
 RUN git clone --recursive https://github.com/ethereum/solidity.git
 WORKDIR /solidity/
 RUN git checkout v0.4.24 # Old version necessary to work???