user can provide global ssh settings

for example in deploy.rb:

      {
         keys: %w(/home/user/.ssh/id_rsa),
         forward_agent: false,
         auth_methods: %w(publickey password)
      }

lib/capistrano/configuration.rb

@@ -59,6 +59,7 @@ module Capistrano
         sshkit.backend.configure do |backend|
           backend.pty                = fetch(:pty)
           backend.connection_timeout = fetch(:connection_timeout)
+          backend.ssh_options        = fetch(:ssh_options) if fetch(:ssh_options)
         end
       end
     end

spec/integration/dsl_spec.rb

@@ -234,6 +234,11 @@ describe Capistrano::DSL do
       dsl.set(:default_env, default_env)
       dsl.set(:pty, true)
       dsl.set(:connection_timeout, 10)
+      dsl.set(:ssh_options, {
+        keys: %w(/home/user/.ssh/id_rsa),
+        forward_agent: false,
+        auth_methods: %w(publickey password)
+      })
       dsl.configure_backend
     end
 
@@ -256,6 +261,13 @@ describe Capistrano::DSL do
     it 'sets the backend connection timeout' do
       expect(backend.connection_timeout).to eq 10
     end
+
+    it 'sets the backend ssh_options' do
+      expect(backend.ssh_options[:keys]).to eq %w(/home/user/.ssh/id_rsa)
+      expect(backend.ssh_options[:forward_agent]).to eq false
+      expect(backend.ssh_options[:auth_methods]).to eq %w(publickey password)
+    end
+
   end
 
 end

spec/lib/capistrano/configuration/server_spec.rb

@@ -137,10 +137,6 @@ module Capistrano
       describe 'assign ssh_options' do
         let(:server) { Server.new('user_name@hostname') }
 
-        # before do
-        #   server
-        # end
-
         context 'defaults' do
           it 'forward agent' do
             expect(server.netssh_options[:forward_agent]).to eq true