run_tests.sh would run tests in serial by default

run_tests.sh would run in serial in parallel
Added concurrency as an argument

Fixed the test case break of test_vm_file_trf_scp_tests

ci_sanity result: http://10.204.216.50/Docs/logs/2.0-2453_2014-11-14_12:41:19/junit-noframes.html

Change-Id: Idd54ee4410e6f632ac3443590b0e5ff88fadcb96
Merge "run_tests.sh would run tests in serial by default"