Run 'rake test' for all installed iOS sdks; good for iOS regressions

run_sdk_tests.rb

showsdks = %x[xcodebuild -showsdks | grep sdk | grep iphonesimulator]
results = []
showsdks.each_line do |sdkline|
  sdk = /-sdk (\S+)/.match(sdkline)[1]
  return_code = system("export IOS_SDK=#{sdk}; rake test")
  results << "#{sdk} success?#{return_code}"
end
results.each do |r|
  puts r
end