tc-testing: better test case file error reporting

tdc.py reads a bunch of test cases in json files.  When a json file
cannot be parsed, tdc just exits and does not run any tests.

This patch will cause tdc to print a message with the file name and
line number, then that file will be ignored and the rest of the tests
will be processed.

Signed-off-by: Brenda J. Butler <bjb@mojatatu.com>
Acked-by: Lucas Bates <lucasb@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>