message: add cores arguemtn to test-all.sh
diff: #!/usr/bin/env bash
  +if [ "$#" -ne 1 ]; then
  +RUNTESTARGS=""
  +else
  +RUNTESTARGS="-j"$1
  +fi
  +
  echo 'Running:'
  echo ' - CmdStan tests'
  echo ' - Stan tests'
  @@ -7,14 +13,14 @@ echo ' - Stan Math Library tests'
  echo ''
  echo '------------------------------------------------------------'
  echo 'CmdStan tests'
  -./runCmdStanTests.py src/test/interface
  +./runCmdStanTests.py $RUNTESTARGS src/test/interface
  echo ''
  echo '------------------------------------------------------------'
  echo 'Stan tests'
  pushd stan/
  -./runTests.py src/test
  +./runTests.py $RUNTESTARGS src/test
  popd
  @@ -22,6 +28,6 @@ echo ''
  echo '------------------------------------------------------------'
  echo 'Stan Math Library tests'
  pushd stan/lib/stan_math/
  -./runTests.py test/unit
  -./runTests.py test/prob
  +./runTests.py $RUNTESTARGS test/unit
  +./runTests.py $RUNTESTARGS test/prob
  popd
  