Only enable download_dep_fail by default for Python >= 2.7.14 for bac…

…kwards compat

easybuild/easyblocks/p/python.py

@@ -132,8 +132,12 @@ def __init__(self, *args, **kwargs):
             easybuild_subdir = log_path()
             self.pythonpath = os.path.join(easybuild_subdir, 'python')
 
+        # Some older ECs break if we enable download_dep_fail due to missing packages
+        # Since Python 2.7.14 (and all Python 3 versions) we usually enable download_dep_fail in the ECs
+        # already so this should not lead to failures
+        download_dep_fail_default = LooseVersion(self.version) >= LooseVersion('2.7.14')
         ext_defaults = {
-            'download_dep_fail': True,
+            'download_dep_fail': download_dep_fail_default,
             # The only installed packages at this point are default installed ones, e.g. pip&setuptools
             # And we want to upgrade them cleanly, i.e. uninstall them
             'pip_ignore_installed': False,