If a domain only has an mx record but no A record it
will trigger a ConnectionError when attempting the
nicknym key lookup.

We need to detect and handle this in the http adapter
already because once the exception is handled by Celluloid
our actor will be terminated.

So now we allow for handing a rescue option to the
adapter with a string that is checked for inclusion in
the error message. If the string is found the exception
will be caught and the adapter returns nil.

We only make use of this when checking the availability
of nicknym so far. That should be the only http request
going out.

http.rb does not do this on its own.

Turns out http.rb does not support celluloid i/o andymore and we were not making
use of it anyway.

Here's what https://github.com/httprb/http/wiki/Thread-Safety says:
(NOTE: this gem previously supported Celluloid::IO, but that support was removed to add the current timeout backend. It may be added back in a future version)

So now we have a plain http.rb adapter and use that as the default.
This prevents actors from crashing in the adapter (as we don't have any).

require all the things we depend upon where we depend upon them.

These warnings were showing on gitlab ci.

$ bundle exec rake test
/usr/local/bin/ruby -w -Ilib:test -I/builds/leap/nickserver/vendor/ruby/2.1.0/gems/rake-11.2.2/lib /builds/leap/nickserver/vendor/ruby/2.1.0/gems/rake-11.2.2/lib/rake/rake_test_loader.rb test/**/*_test.rb
/usr/local/lib/ruby/gems/2.1.0/gems/bundler-1.12.5/lib/bundler/rubygems_integration.rb:468: warning: method redefined; discarding old find_spec_for_exe
/usr/local/lib/ruby/site_ruby/2.1.0/rubygems.rb:261: warning: previous definition of find_spec_for_exe was here
I, [2016-08-26T15:34:46.162843 #325]  INFO -- : Celluloid 0.17.3 is running in BACKPORTED mode. [ http://git.io/vJf3J ]
/builds/leap/nickserver/test/unit/request_handler_test.rb:28: warning: mismatched indentations at 'end' with 'def' at 21
/builds/leap/nickserver/vendor/ruby/2.1.0/gems/celluloid-io-0.17.3/lib/celluloid/io/ssl_socket.rb:22: warning: instance variable @npn_protocols not initialized
/builds/leap/nickserver/vendor/ruby/2.1.0/gems/celluloid-io-0.17.3/lib/celluloid/io/ssl_socket.rb:22: warning: instance variable @npn_select_cb not initialized
Run options: --seed 61653

# Running:

.................../builds/leap/nickserver/vendor/ruby/2.1.0/gems/celluloid-io-0.17.3/lib/celluloid/io/ssl_socket.rb:22: warning: instance variable @npn_protocols not initialized
/builds/leap/nickserver/vendor/ruby/2.1.0/gems/celluloid-io-0.17.3/lib/celluloid/io/ssl_socket.rb:22: warning: instance variable @npn_select_cb not initialized
.../builds/leap/nickserver/vendor/ruby/2.1.0/gems/celluloid-io-0.17.3/lib/celluloid/io/ssl_socket.rb:22: warning: instance variable @npn_protocols not initialized
/builds/leap/nickserver/vendor/ruby/2.1.0/gems/celluloid-io-0.17.3/lib/celluloid/io/ssl_socket.rb:22: warning: instance variable @npn_select_cb not initialized
.................

Finished in 2.029982s, 19.2120 runs/s, 10.8375 assertions/s.

This became possible because we now use celluloid.
Celluloid handles asynchronity without the need for callbacks
or blocks.