pylint: fix simplifiable-if-statement warnings

fix inefficient if statements, enable pylint check

Reviewed-By: Tomas Krizek <tkrizek@redhat.com>
Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>

ipalib/config.py

@@ -455,14 +455,10 @@ class Env(object):
 
         # Determine if running in source tree:
         if 'in_tree' not in self:
-            if (
+            self.in_tree = (
                 self.bin == self.site_packages
                 and path.isfile(path.join(self.bin, 'setup.py'))
-            ):
-                self.in_tree = True
-            else:
-                self.in_tree = False
-
+            )
         if self.in_tree and 'mode' not in self:
             self.mode = 'developer'