def exec(cmd)
      puts "+ [#{Dir.pwd}] #{cmd}" if ENV[VERBOSE]
      res = `#{cmd} 2>&1`
      puts res unless res.empty? if ENV[VERBOSE]
      return res, $?
    end
def exec(cmd)
      puts "+ [#{Dir.pwd}] #{cmd}" if ENV[VERBOSE]
      res = `#{cmd} 2>&1`
      puts res unless res.empty? if ENV[VERBOSE]
      return res, $?
    end
Execute given shell command and return output and exit code
 Allows centralizing logging/output

 === Parameters
 cmd(String):: Command to be run

 === Return
 res, process status(Array):: Pair whose first element is the output of the command
                              and second element is the process exit status