Determine number of cpu cores to use in Vagrant

cpus.rb

# Determines how many cpus the virtual machine should be given. Uses half of
# what's available on the host with a default of 4.
def numvcpus
  begin
    os_cpu_cores / 2
  rescue
    4
  end
end

# Get the number of logical cpu cores.
def os_cpu_cores
  case RbConfig::CONFIG['host_os']
  when /darwin/
    Integer(`sysctl -n hw.ncpu`)
  when /linux/
    Integer(`cat /proc/cpuinfo | grep processor | wc -l`)
  else
    raise StandardError, "Unsupported platform"
  end
end

puts "Use %s cores.", numvcpus