Docker image fixes (#31)

* Don't create the PyPi cache in the docker image

Creating the PyPi cache in a docker image only increase the image size
and is useless, so disable it.

* Add build args to allow selecting the base docker image

Add build args to allow selecting the base docker image without having
to edit the Dockerfile. This is especially usefull for automated
builds were editing files is not an option.

Author: AlbanBedel

Dockerfile

@@ -1,7 +1,10 @@
-FROM netboxcommunity/netbox:latest-ldap
+ARG FROM_IMAGE=netboxcommunity/netbox
+ARG FROM_TAG=latest-ldap
+ARG FROM=${FROM_IMAGE}:${FROM_TAG}
+FROM ${FROM}
 
 COPY ./nextbox_ui_plugin /source/nextbox-ui-plugin/nextbox_ui_plugin/
 COPY ./setup.py /source/nextbox-ui-plugin/
 COPY ./MANIFEST.in /source/nextbox-ui-plugin/
 COPY ./README.md /source/nextbox-ui-plugin/
-RUN pip3 install nextbox-ui-plugin
+RUN pip3 install --no-cache-dir nextbox-ui-plugin