python_build: Make `verify_python` verify `pythonX.Y' suffix (#3459)

* Fix erroneous use in tests that didn't show until now

plugins/python-build/bin/python-build

@@ -2101,10 +2101,12 @@ build_package_symlink_version_suffix() {
 
 verify_python() {
   build_package_symlink_version_suffix
+  
+  local python_bin="${PYTHON_BIN%/*}/python${1:?}"
 
-  if [ ! -x "${PYTHON_BIN}" ]; then
+  if [ ! -x "${python_bin}" ]; then
     { colorize 1 "ERROR"
-      echo ": invalid Python executable: ${PYTHON_BIN}"
+      echo ": invalid Python executable: ${python_bin}"
       echo
       echo "The python-build could not find proper executable of Python after successful build."
       echo "Please open an issue for future improvements."

plugins/python-build/test/pyenv_ext.bats

@@ -233,7 +233,7 @@ OUT
   chmod +x "${INSTALL_ROOT}/bin/python3.4-config"
 
   TMPDIR="$BATS_TEST_TMPDIR" run_inline_definition <<OUT
-verify_python python3.4
+verify_python 3.4
 OUT
   assert_success
 
@@ -259,7 +259,7 @@ OUT
 echo "PYTHON_CONFIGURE_OPTS_ARRAY=(\${PYTHON_CONFIGURE_OPTS_ARRAY[@]})"
 echo "PYTHON_CONFIGURE_OPTS=(\${PYTHON_CONFIGURE_OPTS})"
 echo "CONFIGURE_OPTS=(\${CONFIGURE_OPTS})"
-verify_python python3.4
+verify_python 3.4
 OUT
   assert_success
   assert_output <<EOS