check-hardware-fail errors when dmesg contains characters not valid for utf-8

[cwjohnston]

As reported by a Sensu Enterprise user:

bash-4.1$ /opt/sensu/embedded/bin/ruby /opt/sensu/embedded/bin/check-hardware-fail.rb
Check failed to run: invalid byte sequence in UTF-8, 
["/opt/sensu/embedded/lib/ruby/gems/2.4.0/gems/sensu-plugins-hardware-1.1.0/bin/check-hardware-fail.rb:55:in `[]'", "/opt/sensu/embedded/lib/ruby/gems/2.4.0/gems/sensu-plugins-hardware-1.1.0/bin/check-hardware-fail.rb:55:in `block in run'", "/opt/sensu/embedded/lib/ruby/gems/2.4.0/gems/sensu-plugins-hardware-1.1.0/bin/check-hardware-fail.rb:55:in `select'", "/opt/sensu/embedded/lib/ruby/gems/2.4.0/gems/sensu-plugins-hardware-1.1.0/bin/check-hardware-fail.rb:55:in `run'", "/opt/sensu/embedded/lib/ruby/gems/2.4.0/gems/sensu-plugin-1.4.5/lib/sensu-plugin/cli.rb:58:in `block in '"]

I think we can address this with some input sanitization, as described here https://robots.thoughtbot.com/fight-back-utf-8-invalid-byte-sequences