Fix version installs with justhub repo

If we specify a version of the package in the justhub repo, we need to make sure
we specify the same version for both the haskell meta package and the
haskell-min meta package. Otherwise it will still install the latest version of
ghc. Added tests to ensure the correct ghc version gets installed.
Fix typo
Add test to ensure the ghc binary exists and executable
Code cleanup and optimization
Check if the file exists before we try to get version information from it
Merge pull request #2 from osuosl-cookbooks/ramereth/fix-justhub-version-install

Fix version installs with justhub repo