collect: check python version and not just presence of subprocess32

promise are executed with the python interpreter running `slapos node
instance` and not with the python interpreter from the software. This
might be wrong.

When running slapos node on python3, we may be running scripts generated
for python3, ie. with subprocess32 installed. This becomes a problem
with python3.6 as it fails importing subprocess32

slapos/collect/temperature/__init__.py

 from __future__ import print_function
 
 from multiprocessing import Process, active_children, cpu_count, Pipe
-try:
-  import subprocess32 as subprocess
-except ImportError:
+
+# When we run slapos node on python3 and install some software using python2,
+# subprocess32 will be installed, because the working set is generated for
+# the buildout python and not the python running slapos node instance.
+# To workaround this, we don't check the presence of subprocess32 egg, but
+# the fact that we run on python3.
+import six
+if six.PY2:
+  import subprocess32 as subprocess #  pylint: disable=import-error
+else:
   import subprocess
+
 import os
 import signal
 import sys