Add script to check test-discovery

We now check if test discovery in scripts/ and serial-scripts/ pass
before proceeding to run any tests.
If test-discovery fails, non-zero value is returned

Also, removed some old,unused test-script files

Change-Id: I9f547e0e44730bdf141fe410c83bf61e3ee87a4e
Merge "Add script to check test-discovery"