python/audit2allow: allow using audit2why as non-root user

Importing sepolicy as non-root on a system with SELinux causes the
following exception to be raised:

    ValueError: No SELinux Policy installed

Ignore this when using audit2why, which allows using it with option
--policy as a non-root user.

Signed-off-by: Nicolas Iooss <nicolas.iooss@m4x.org>

python/audit2allow/audit2allow

@@ -242,7 +242,10 @@ class AuditToPolicy:
 
     def __output_audit2why(self):
         import selinux
+        try:
             import sepolicy
+        except (ImportError, ValueError):
+            sepolicy = None
         for i in self.__parser.avc_msgs:
             rc = i.type
             data = i.data
@@ -262,10 +265,12 @@ class AuditToPolicy:
                 if len(data) > 1:
                     print("\tOne of the following booleans was set incorrectly.")
                     for b in data:
+                        if sepolicy is not None:
                             print("\tDescription:\n\t%s\n" % sepolicy.boolean_desc(b[0]))
                         print("\tAllow access by executing:\n\t# setsebool -P %s %d" % (b[0], b[1]))
                 else:
                     print("\tThe boolean %s was set incorrectly. " % (data[0][0]))
+                    if sepolicy is not None:
                         print("\tDescription:\n\t%s\n" % sepolicy.boolean_desc(data[0][0]))
                     print("\tAllow access by executing:\n\t# setsebool -P %s %d" % (data[0][0], data[0][1]))
                 continue