contrib: Add py.test to builder Dockerfiles

With the previous commit this enables py.test on travis, which should
give us some better way of hunting down bugs on travis.

Signed-off-by: Christian Decker <decker.christian@gmail.com>

contrib/Dockerfile.builder

@@ -23,6 +23,7 @@ RUN apt-get -qq update && \
 	valgrind \
 	net-tools \
 	python3-pip \
+	python-pkg-resources \
 	wget && \
 	rm -rf /var/lib/apt/lists/*
 
@@ -32,4 +33,4 @@ RUN cd /tmp/ && \
     mv /tmp/bitcoin-0.15.0/bin/bitcoin* /usr/local/bin/ && \
     rm -rf bitcoin.tar.gz /tmp/bitcoin-0.15.0
 
-RUN pip3 install python-bitcoinlib==0.7.0
+RUN pip3 install python-bitcoinlib==0.7.0 pytest==3.0.5 setuptools==36.6.0

contrib/Dockerfile.builder.i386

@@ -23,6 +23,7 @@ RUN apt-get -qq update && \
 	valgrind \
 	net-tools \
 	python3-pip \
+	python-pkg-resources \
 	wget && \
 	rm -rf /var/lib/apt/lists/*
 
@@ -32,4 +33,4 @@ RUN cd /tmp/ && \
     mv /tmp/bitcoin-0.15.0/bin/bitcoin* /usr/local/bin/ && \
     rm -rf bitcoin.tar.gz /tmp/bitcoin-0.15.0
 
-RUN pip3 install python-bitcoinlib==0.7.0
+RUN pip3 install python-bitcoinlib==0.7.0 pytest==3.0.5 setuptools==36.6.0