Backport paramiko 1.8.0 requirement to Folsom.

Require paramiko >= 1.8.0

There is a well-known bug in the Paramiko SSH library that causes
these Exceptions:
SSHException: Error connecting via ssh: PID check failed. RNG must be
re-initialized after fork(). Hint: Try Random.atfork()

This bug has been fixed in Paramiko, and therefore we should require
the newer version for Cinder drivers that use Paramiko to function
properly.

Change-Id: Ia14b7b72393e2a2482ebde418b5477934779bf13
Fixes: bug 1150720

tools/pip-requires

@@ -13,7 +13,7 @@ PasteDeploy==1.5.0
 paste
 sqlalchemy-migrate>=0.7.2
 suds==0.4
-paramiko
+paramiko>=1.8.0
 Babel>=0.9.6
 iso8601>=0.1.4
 setuptools_git>=0.4