Update CI build scripts for Python

.ci/python.build

@@ -1,7 +1,11 @@
 #!/bin/bash
 set -e
 
+python3 -m venv .venv
+. .venv/bin/activate
+
+pip install setuptools tox
+
 ./autogen.sh
-./configure PYTHON=/usr/bin/python3 CC=clang CXX=clang++ CXXFLAGS='-O1'
+./configure CC=clang CXX=clang++ CXXFLAGS='-O1'
 make -C Python
-make -C Python wheel

.ci/python.check

@@ -1,9 +1,10 @@
 #!/bin/bash
 set -e
 
+. .venv/bin/activate
+
 make -C Python check
 
-. .venv/bin/activate
 for i in Python/examples/*.py
 do
     echo "$i"

.ci/python.install

@@ -1,8 +1,8 @@
 #!/bin/bash
 set -e
 
-python3 -m venv .venv
 . .venv/bin/activate
+
 pip install Python/dist/QuantLib-*.whl
 grep -v QuantLib binder/requirements.txt > Python/examples/requirements.txt
 pip install -r Python/examples/requirements.txt