Skip test if cookiecutter is not installed

Author: dnerini

pysteps/tests/test_plugins_support.py

@@ -5,9 +5,12 @@
 https://github.com/pySTEPS/cookiecutter-pysteps-plugin
 """
 import os
+import pytest
 import subprocess
 import sys
 import tempfile
+
+__ = pytest.importorskip("cookiecutter")
 from cookiecutter.main import cookiecutter
 
 PLUGIN_TEMPLATE_URL = "https://github.com/pysteps/cookiecutter-pysteps-plugin"