Use Chef's file_cache_path rather than hardcoded /tmp

In order to work when well with other components that use file_cache_path
like vagrant-cachier when file_cache_path is relocated.
Cosmetic change to be consistent in use of symbols when referencing attributes
Merge pull request #2 from russellcardullo/use_symbols_consistently

Cosmetic change to be consistent in use of symbols
Merge pull request #1 from russellcardullo/use_chef_cache_for_tmp

Use Chef's file_cache_path rather than hardcoded /tmp
change default mesos install directory from /tmp to /opt