Catch Error Raised When No Hosts Are Found

[jonmchan]

Catch and print friendly error message for the following error when no hosts are found:

/usr/local/var/rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/ipaws-0.3.0/lib/ipaws/eb_commands.rb:162:in `eb_ssh': undefined method `[]' for nil:NilClass (NoMethodError)
    from /usr/local/var/rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/ipaws-0.3.0/bin/ipaws:83:in `ssh'
    from /usr/local/var/rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/thor-0.19.1/lib/thor/command.rb:27:in `run'
    from /usr/local/var/rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/thor-0.19.1/lib/thor/invocation.rb:126:in `invoke_command'
    from /usr/local/var/rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/thor-0.19.1/lib/thor.rb:359:in `dispatch'
    from /usr/local/var/rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/thor-0.19.1/lib/thor/base.rb:440:in `start'
    from /usr/local/var/rbenv/versions/2.2.4/lib/ruby/gems/2.2.0/gems/ipaws-0.3.0/bin/ipaws:160:in `<top (required)>'
    from /usr/local/var/rbenv/versions/2.2.4/bin/ipaws:23:in `load'
    from /usr/local/var/rbenv/versions/2.2.4/bin/ipaws:23:in `<main>'