Add testing function for ovs_switch and utils

[hwchiu]

• Add new dependency for testing (I use testify)
• Add utils_test to testing for utils
• Add ovs_switch_test to testing for ovs_switch
• ovs_switch.go provide function to delete itself()
• Add travis to perform go test and coverage
• Modify README to add travis/coverage/godocs badge

[hwchiu]

Reopen after fixing CI

[hwchiu]

close to fix the rebase problem.