Only invoke .lower() on non-None protocols

When using source group based security group rules (rather than CIDR
based ones), it's permissible to not set a protocol and port. However,
Nova would always try to convert the protocol to lower case, which would
fail if the protocol wasn't set.

Fixes bug 1010514

Change-Id: I9b1519a52ececd16a497acebfe022508cbe96126

.mailmap

@@ -60,6 +60,7 @@
 <sandy.walsh@rackspace.com> <sandy@sandywalsh.com>
 <sleepsonthefloor@gmail.com> <root@tonbuntu>
 <soren.hansen@rackspace.com> <soren@linux2go.dk>
+<soren@linux2go.dk> <sorhanse@cisco.com>
 <throughnothing@gmail.com> <will.wolf@rackspace.com>
 <tim.simpson@rackspace.com> <tim.simpson4@gmail.com>
 <todd@ansolabs.com> <todd@lapex>