update and simplify pyzmq draft example script

- use bundled libzmq, now that we run a fully cmake build
- use --no-cache to avoid installing previous local builds

examples/draft/install.sh

@@ -2,28 +2,19 @@
 
 # example script for installing libzmq and pyzmq with draft support
 
-# 1. install libzmq with draft enabled
-ZMQ_VERSION=4.3.4
-PREFIX=${PREFIX:-/usr/local}
-PYZMQ=${PYZMQ:-pyzmq}
-CPU_COUNT=${CPU_COUNT:-$(python3 -c "import os; print(os.cpu_count())")}
+# tell pyzmq to build bundled libzmq with cmake
+# (alternately, install and build libzmq with drafts enabled)
+export ZMQ_PREFIX=bundled
 
-set -ex
-echo "installing libzmq to $PREFIX"
-wget https://github.com/zeromq/libzmq/releases/download/v${ZMQ_VERSION}/zeromq-${ZMQ_VERSION}.tar.gz -O libzmq.tar.gz
-tar -xzf libzmq.tar.gz
-cd zeromq-${ZMQ_VERSION}
-./configure --prefix=${PREFIX} --enable-drafts
-make -j${CPU_COUNT} && make install
+# tell pyzmq to build libzmq with draft support
+export ZMQ_DRAFT_API=1
 
-# install pyzmq with drafts enabled
+# install pyzmq
 # By specifying ``--no-binary pyzmq``, pip knows to not install wheels, and will compile pyzmq from source.
+# --no-cache prevents installing a previously cached local build of pyzmq
 
-echo "installing ${PYZMQ}"
-export ZMQ_PREFIX=${PREFIX}
-export ZMQ_DRAFT_API=1
-
-pip install -v --no-binary pyzmq --pre ${PYZMQ}
+echo "installing pyzmq"
+pip install -v --no-cache --no-binary pyzmq pyzmq
 
 cat << END | python3
 import sys