Display system_info output if it exists
Change anticipated text file location

After looking at http://www.wikiwand.com/en/Filesystem_Hierarchy_Standard
and some discussion about Homebrew unlikely to be happy with
`/usr/local` being used, we settle with
`/usr/share/travis/sytem_info` as a better location going forward.
system_info: fix the file name, add outputting the build script language
add an extra newline after the system_info fold
system_info: output dist and group if given
system_info: only output attrs that have a value
system_info: fix the message for language, group, and dist
Merge pull request #326 from travis-ci/ha-feature-system-info

Display /usr/share/travis/sytem_info in fold if it exists