Cap minimum version of net-ssh gem

Version 3.2.0 non-compatible with several other deps

PROD-37075

Change-Id: Ie98c0115788133637ddbbb5778ba1f5dc66bb118
diff --git a/Gemfile b/Gemfile
index 68c8823..49e6ca0 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,5 +1,6 @@
 source 'https://rubygems.org'
 ruby '>=2.4.0'
+gem 'net-ssh', '>4.0'
 gem 'rake'
 gem 'test-kitchen', '<2.0.0'
 if File.exist?('.kitchen.openstack.yml') then