Micro-optimization: replace s.find(x)!=-1 with x in s

timeit shows a speedup of ~3x on Python 2.7.5 x86_64.
It also makes the code a bit shorter.

library/system/open_iscsi

@@ -138,7 +138,7 @@ def iscsi_get_cached_nodes(module, portal=None):
     # older versions of scsiadm don't have nice return codes
     # for newer versions see iscsiadm(8); also usr/iscsiadm.c for details
                                   # err can contain [N|n]o records...
-    elif rc == 21 or (rc == 255 and err.find("o records found") != -1):
+    elif rc == 21 or (rc == 255 and "o records found" in err):
         nodes = []
     else:
         module.fail_json(cmd=cmd, rc=rc, msg=err)