tc-testing: tdc.py: ignore errors when decoding stdout/stderr

[ Upstream commit 5aaf6428526bcad98d6f51f2f679c919bb75d7e9 ]

Prevent exceptions from being raised while decoding output
from an executed command. There is no impact on tdc's
execution and the verify command phase would fail the pattern
match.

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