Fixes #14461 - removed :method_missing from Proxy::Settings::Plugin
OpenStruct always returned 'nil' when calling methods for non-existing keys. Before ruby 2.3 methods for keys were defined during OpenStruct instantiation. Starting with ruby 2.3 methods for members of the OpenStruct are defined lazily, via method_missing. Our override of the method was breaking OpenStruct (and as a consequence Proxy::Settings::Plugin).
Related issues
Bug #14461: Smart proxy fails to load any modules when running under ruby 2.3
Fixes #14461 - removed :method_missing from Proxy::Settings::Plugin