Update Travis Tests to run platforms in parallel (#11256)

.travis.yml

buildroot/bin/env_backup

buildroot/bin/env_clean

buildroot/bin/env_restore

buildroot/bin/restore_configs

buildroot/share/tests/DUE_tests

buildroot/share/tests/LPC1768_tests

buildroot/share/tests/STM32F1_tests

buildroot/share/tests/megaatmega2560_tests

buildroot/share/tests/start_tests

buildroot/share/tests/teensy35_tests