Revert "use modern paramiko"

This reverts commit 76e1b09.

I see lots of these failures:

2015-09-06T00:02:43.199 ERROR:paramiko.transport:SSHException: Key-exchange timed out waiting for key negotiation

setup.py

@@ -42,7 +42,7 @@
                       'configobj',
                       'six >= 1.9', # python-openstackclient won't work properly with less
                       'httplib2',
-                      'paramiko >= 1.15.1',
+                      'paramiko < 1.8',
                       'pexpect',
                       'requests >= 2.3.0',
                       'raven',