Close paramiko connections explicitly

We have observed at least one case in the wild where an unreadable ssh
private key file results in thousands of connections being made to
Gerrit over a relatively short period of time. We expect this is due to
newer paramiko behavior that requires you explicitly close connections
(even when they fail).

Fix this by adding explicit client closes.

Change-Id: I713cb704ac24db5d38cd9c0c2d60962dca647f75
Story: 2000923
1 file changed