Alpine latest provide a separate package for pip

git-svn-id: https://redmine.imt-atlantique.fr/svn/xaal/code/Python/branches/0.7@2484 b32b6428-25c9-4566-ad07-03861ab6144f

docker/xaal-shell/Dockerfile

 FROM alpine:latest
 RUN apk update
-RUN apk add --no-cache  python3 python3-dev subversion libsodium-dev git g++ musl-dev tmux file
+RUN apk add --no-cache python3 python3-dev py3-pip subversion libsodium-dev git g++ musl-dev tmux file
 RUN pip3 install --upgrade pip
     
 # due to a bug in current ujson on alpine, we need to use the git