prune: fix some UnicodeDecodeError on python3 with binary scripts

Some softwares have some binary executables in builout bin folder,
reading them as text can fail. In this case we can ignore them.

slapos/cli/prune.py

@@ -217,7 +217,10 @@ def getUsageSignatureFromSoftwareAndSharedPart(
       signatures[installed_cfg] = f.read()
   for script in glob.glob(os.path.join(software_root, '*', 'bin', '*')):
     with open(script) as f:
-      signatures[script] = f.read()
+      try:
+        signatures[script] = f.read()
+      except UnicodeDecodeError:
+        logger.debug("Skipping script %s that could not be decoded", script)
   if shared_root:
     for shared_signature in glob.glob(os.path.join(shared_root, '*', '*',
                                                    '.*signature')):

slapos/tests/test_prune.py

@@ -31,6 +31,7 @@ import os
 import shutil
 import unittest
 import slapos.client
+import six
 
 try:
   import mock
@@ -139,11 +140,19 @@ class TestPrune(unittest.TestCase):
     script = os.path.join(fake_software_path, 'bin', 'buildout')
     with open(script, 'w') as f:
       f.write('#!{}'.format(used_in_script))
+    # bin/ can also contain binary executables, this should not cause problems
+    binary_script = os.path.join(fake_software_path, 'bin', 'binary')
+    with open(binary_script, 'wb') as f:
+      f.write(b'\x80')
     do_prune(self.logger, self.config, False)
     self.assertTrue(os.path.exists(used_in_script))
     self.assertFalse(os.path.exists(not_used))
     self.logger.warning.assert_called_with(
         'Unusued shared parts at %s%s', not_used, ' ... removed')
+    if six.PY3:
+      self.logger.debug.assert_any_call(
+        'Skipping script %s that could not be decoded', binary_script)
+
 
   def test_shared_part_used_in_recursive_instance(self):
     used_in_software_from_instance = self._createSharedPart('used_in_software_from_instance')