[ubuntu] disable pip cache dir by default

jupyterhub/base/Dockerfile

@@ -18,7 +18,7 @@ RUN curl -sL https://deb.nodesource.com/setup_10.x | bash - && \
         openjdk-11-jre-headless && \
     apt-get clean
 
-RUN python${PYTHON_VERSION} -m pip --no-cache-dir install \
+RUN python${PYTHON_VERSION} -m pip install \
         jupyterlab \
         jupyterhub \
         ipympl \
@@ -33,20 +33,20 @@ RUN python${PYTHON_VERSION} -m pip --no-cache-dir install \
         jupyterlab-execute-time \
     && \
     python${PYTHON_VERSION} -m jupyter labextension install @ryantam626/jupyterlab_code_formatter && \
-    python${PYTHON_VERSION} -m pip --no-cache-dir install jupyterlab_code_formatter && \
+    python${PYTHON_VERSION} -m pip install jupyterlab_code_formatter && \
     python${PYTHON_VERSION} -m jupyter serverextension enable --sys-prefix --py jupyterlab_code_formatter && \
-    python${PYTHON_VERSION} -m pip --no-cache-dir install black isort && \
-    python${PYTHON_VERSION} -m pip --no-cache-dir install jupyterlab-git && \
+    python${PYTHON_VERSION} -m pip install black isort && \
+    python${PYTHON_VERSION} -m pip install jupyterlab-git && \
     python${PYTHON_VERSION} -m jupyter lab build
 
 RUN mkdir -p /usr/local/venv && \
     python${PYTHON_VERSION} -m venv /usr/local/venv/default && \
     . /usr/local/venv/default/bin/activate && \
-    python${PYTHON_VERSION} -m pip --no-cache-dir install --upgrade \
+    python${PYTHON_VERSION} -m pip install --upgrade \
         pip==${PYTHON_PIP_VERSION} \
         setuptools==${PYTHON_SETUPTOOLS_VERSION} && \
-    pip --no-cache-dir install tensorflow==1.15.3 && \
-    pip --no-cache-dir install \
+    pip install tensorflow==1.15.3 && \
+    pip install \
         wheel \
         black \
         isort \

ubuntu/pip.conf

@@ -2,3 +2,4 @@
 extra-index-url = https://agki-nas01.imp.fu-berlin.de:30443/
 cert = /etc/ssl/certs/ca-certificates.crt
 disable-pip-version-check = true
+no-cache-dir = false