tc-testing: Allow tdc plugins to see test case data

Instead of only passing the test case name and ID, pass the
entire current test case down to the plugins. This change
allows plugins to start accepting commands and directives
from the test cases themselves, for greater flexibility
in testing.

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