disable insert_key=true by default

https://github.com/mitchellh/vagrant/issues/2608


NOTE: this can be done globally for your own account as well:

  @TomyLobo:

  Not exactly true, you can also put this in a ~/.vagrant.d/Vagrantfile to apply it to all machines on your desktop.

  config.ssh.insert_key = false

https://github.com/mitchellh/vagrant/pull/4707#issuecomment-132910396

--- vagrant-1.7.1/plugins/kernel_v2/config/ssh_connect.rb~	2014-12-12 11:36:39.000000000 +0200
+++ vagrant-1.7.1/plugins/kernel_v2/config/ssh_connect.rb	2015-02-01 20:47:27.907465716 +0200
@@ -23,7 +23,7 @@
         @private_key_path = nil if @private_key_path == UNSET_VALUE
         @username         = nil if @username == UNSET_VALUE
         @password         = nil if @password == UNSET_VALUE
-        @insert_key       = true if @insert_key == UNSET_VALUE
+        @insert_key       = false if @insert_key == UNSET_VALUE
         @keys_only        = true if @keys_only == UNSET_VALUE
         @paranoid         = false if @paranoid == UNSET_VALUE
         @verify_host_key  = false if @verify_host_key == UNSET_VALUE