Handle recent breaking changes in upstream pip (#1355)

Drop support for python2, while we are at it.

build-any-ib.sh

@@ -30,15 +30,8 @@ export PYTHONUSERBASE=$(mktemp -d)
 export PATH=$PYTHONUSERBASE/bin:$PATH
 export LD_LIBRARY_PATH=$PYTHONUSERBASE/lib:$LD_LIBRARY_PATH
 # Set the default python and pip depending on the architecture...
-case $ARCHITECTURE in
-  slc6*) PIP=pip PYTHON=python ;;
-  *) PIP=pip3 PYTHON=python3 ;;
-esac
-# ...and override it if PYTHON_VERSION is specified.
-case "$PYTHON_VERSION" in
-  2) PIP=pip2 PYTHON=python2 ;;
-  3) PIP=pip3 PYTHON=python3 ;;
-esac
+PIP=pip3 PYTHON=python3
+$PIP install --user --upgrade pip
 $PIP install --user --upgrade "${ALIBUILD_SLUG:+git+https://github.com/}${ALIBUILD_SLUG:-alibuild}"
 type aliBuild