Add specs for Rex::Arch::Sparc

Verification
-----------

- [ ] Be sure which travis is green
- [ ] Run the specs locally and ensure all the test pass

```
$ rspec spec/lib/rex/arch/sparc_spec.rb


WARNING: Cucumber-rails required outside of env.rb.  The rest of loading is being defered until env.rb is called.
  To avoid this warning, move 'gem cucumber-rails' under only group :test in your Gemfile
Rex::Arch::Sparc .................

Finished in 0.02408 seconds
17 examples, 0 failures

Randomized with seed 43490




Coverage report generated for RSpec to /Users/jvazquez/Projects/Code/metasploit-framework/coverage. 16369 / 92717 LOC (17.65%) covered.
```