#980: IOError: closed stream

skip errors when waiting for the channel to complete

```sh
[GEM_ROOT]/gems/net-ssh-2.2.2/lib/net/ssh/ruby_compat.rb:22:in `select'
[GEM_ROOT]/gems/net-ssh-2.2.2/lib/net/ssh/ruby_compat.rb:22:in `io_select'
[GEM_ROOT]/gems/net-ssh-2.2.2/lib/net/ssh/transport/packet_stream.rb:73:in `available_for_read?'
[GEM_ROOT]/gems/net-ssh-2.2.2/lib/net/ssh/transport/packet_stream.rb:85:in `next_packet'
[GEM_ROOT]/gems/net-ssh-2.2.2/lib/net/ssh/transport/session.rb:171:in `block in poll_message'
[GEM_ROOT]/gems/net-ssh-2.2.2/lib/net/ssh/transport/session.rb:166:in `loop'
[GEM_ROOT]/gems/net-ssh-2.2.2/lib/net/ssh/transport/session.rb:166:in `poll_message'
[GEM_ROOT]/gems/net-ssh-2.2.2/lib/net/ssh/connection/session.rb:451:in `dispatch_incoming_packets'
[GEM_ROOT]/gems/net-ssh-2.2.2/lib/net/ssh/connection/session.rb:213:in `preprocess'
[GEM_ROOT]/gems/net-ssh-2.2.2/lib/net/ssh/connection/session.rb:197:in `process'
[GEM_ROOT]/gems/net-ssh-2.2.2/lib/net/ssh/connection/session.rb:161:in `block in loop'
[GEM_ROOT]/gems/net-ssh-2.2.2/lib/net/ssh/connection/session.rb:161:in `loop'
[GEM_ROOT]/gems/net-ssh-2.2.2/lib/net/ssh/connection/session.rb:161:in `loop'
[GEM_ROOT]/gems/net-ssh-2.2.2/lib/net/ssh/connection/channel.rb:269:in `wait'
[GEM_ROOT]/bundler/gems/vagrant-2379d0f767ca/plugins/communicators/ssh/communicator.rb:257:in `shell_execute'
[GEM_ROOT]/bundler/gems/vagrant-2379d0f767ca/plugins/communicators/ssh/communicator.rb:58:in `block in execute'
[GEM_ROOT]/bundler/gems/vagrant-2379d0f767ca/plugins/communicators/ssh/communicator.rb:130:in `connect'
[GEM_ROOT]/bundler/gems/vagrant-2379d0f767ca/plugins/communicators/ssh/communicator.rb:57:in `execute'
```