Is539/master build fails (#540)

* minor cleanup

* Fixed storage Dockerfile image build:
 - Added workaround for pypa/pip#6197
 - Froze python2 requirements (virtualenv py2.7 would fail to install numpy)

* Fixes director Dockerfile using same workaround in pip as with storage

* Applies pip workaround to sidecar Dockerfile

* Applies pip workaround to webserver Dockerfile

* Applied pip workaround to backend dynamic services

* pip compiled py27.in -> py27.txt (pip-tools)
 Changes to be committed:
	new file:   services/storage/requirements/py27.in
	modified:   services/storage/requirements/py27.txt

.travis.yml

@@ -127,7 +127,7 @@ jobs:
 
     # test python, linting ----------------------------------------------------------------------
     - stage: unit testing
-      name: Python linting
+      name: python linting
       language: python
       python:
         - "3.6"

services/dy-2Dgraph/use-cases/cc/Dockerfile

@@ -11,7 +11,9 @@ USER $NB_USER
 
 # install requirements --------------------------------------------------------
 COPY --chown=jovyan:users cc/requirements.txt .
-RUN pip install --no-cache-dir -r requirements.txt
+# TODO: tmp workaround for https://github.com/pypa/pip/issues/6197
+RUN pip --cache-dir=/pipcache install -r requirements.txt &&\
+    rm -rf /pipcache
 # prepare for booting ---------------------------------------------------------
 COPY --chown=jovyan:users docker /docker
 # set of arguments to copy the right notebook ---------------------------------
@@ -36,4 +38,4 @@ ARG NOTEBOOK_NAME
 ARG NOTEBOOK_FOLDER_NAME
 # copy the notebook in the image
 COPY --chown=jovyan:users cc/${NOTEBOOK_FOLDER_NAME}/${NOTEBOOK_NAME} ${NOTEBOOK_NAME}
-ENTRYPOINT [ "/bin/bash", "/docker/boot.sh" ]
+ENTRYPOINT [ "/bin/bash", "/docker/boot.sh" ]

services/dy-2Dgraph/use-cases/kember/Dockerfile

@@ -4,7 +4,10 @@ LABEL maintainer="sanderegg"
 
 # install requirements --------------------------------------------------------
 COPY --chown=jovyan:users kember/requirements.txt .
-RUN pip install --no-cache-dir -r requirements.txt
+# TODO: tmp workaround for https://github.com/pypa/pip/issues/6197
+RUN pip --cache-dir=/pipcache install -r requirements.txt &&\
+    rm -rf /pipcache
+
 
 # prepare for booting ---------------------------------------------------------
 COPY --chown=jovyan:users docker /docker
@@ -29,4 +32,4 @@ FROM common AS production
 ARG NOTEBOOK_NAME
 # copy the notebook in the image
 COPY --chown=jovyan:users kember/${NOTEBOOK_NAME} ${NOTEBOOK_NAME}
-ENTRYPOINT [ "/bin/bash", "/docker/boot.sh" ]
+ENTRYPOINT [ "/bin/bash", "/docker/boot.sh" ]