msfpro compatibility

[MSP-10964](https://jira.tor.rapid7.com/secure/RapidBoard.jspa?rapidView=84&selectedIssue=MSP-10964)

Allow msfpro to load msfconsole.  Additionally, allow RAILS_ENV or RAILS_ENV and --environment to be used in addition to just `--environment`, with `--environment` taking precedence.

# Verification Steps

## Default

- [x] `./msfconsole`
- [x] `irb`
- [x] VERIFY `Rails.env` is `'production'` by default
- [x] `exit`
- [x] `exit`

## RAILS_ENV

- [x] `RAILS_ENV=development ./msfconsole`
- [x] `irb`
- [x] VERIFY `Rails.env` is `'development'`, indicating the RAILS_ENV can override the default
- [x] `exit`
- [x] `exit`

## --environment

- [x] `./msfconsole --environment development`
- [x] `irb`
- [x] VERIFY `Rails.env` is `'development'`, indicating `--environment` can override the default
- [x] `exit`
- [x] `exit`

## RAILS_ENV and --environment

- [x] `RAILS_ENV=test ./msfconsole --environment development`
- [x] `irb`
- [x] VERIFY `Rails.env` is `'development'`, indicating that `--environment` can override `RAILS_ENV`
- [x] `exit`
- [x] `exit`

## `rake spec`