Fix ordering bug in test #150.

Test hard-codes a string containing '\n' and then expects echo
to interpret it as a newline, which it does not without the -e option.

This fixes flaky test runs like the below:
>>> Running /root/src/github.com/weaveworks/weave/test/150_connect_forget_2_test.sh on [138.68.153.213 138.68.149.186]
>>> Test /root/src/github.com/weaveworks/weave/test/150_connect_forget_2_test.sh finished after 12.4 secs with error: exit status 1
test #5 "direct_peers 138.68.149.186 | sort" failed:
  expected "138.68.153.213\n138.68.149.186"
  got "138.68.149.186\n138.68.153.213"

test/150_connect_forget_2_test.sh

@@ -11,7 +11,7 @@ direct_peers() {
 }
 
 assert_peers() {
-  assert "direct_peers $1 | sort" "$(echo "$2" | sort)"
+  assert "direct_peers $1 | sort" "$(echo -e "$2" | sort)"
 }
 
 start_suite "Connecting and forgetting routers after launch"