Added tests for Pry::Command::ReloadCode#reload_object and Pry::Command:...

...:ReloadCode#process

Added test for Pry::Command::ReloadCode#reload_code and Pry::Command::ReloadCode#process in response to #1204

Used `pry_eval` to make test simpler and more robust, as advised by @ConradIrwin in https://github.com/pry/pry/pull/1212.

reload_code_spec.rb now tests all paths of `process` and tests `reload-code`.