These are changes in run_tests.sh

1.To run sanity
./run_tests.sh -s

2.To run tests from a specific directory/set of directories
./run_tests.sh -F 'neutron discovery_regression'

3.To run  tests with specific tags
./run_tests.sh -T tag1 tag2 etc

4.To run tests sanity and along with some specific directory
./run_tests.sh -s -F 'discovery_regression'

5.If either tags or directory not passed, entire tests would be run