Remove pip cache dir

Dockerfile

@@ -23,7 +23,7 @@ RUN apt-get update \
             python-urllib3 \
             rsync \
             tahoe-lafs \
-        && pip install -U boto b2 \
+        && pip install -U --no-cache-dir boto b2 \
         && apt-get autoremove -y python-pip \
         && apt-get clean \
         && rm -rf /var/apt/lists/*

Dockerfile.armhf

@@ -17,8 +17,8 @@ RUN apt-get update \
             python-urllib3 \
             rsync \
             tahoe-lafs \
-        && pip install -U setuptools \
-        && pip install -U boto b2 \
+        && pip install --no-cache-dir -U setuptools \
+        && pip install --no-cache-dir -U boto b2 \
         && apt-get remove -y python-pip \
         && apt-get install -y --no-install-recommends \
             python-swiftclient \