test/py: ignore console read exceptions after test failure

test/py: ignore console read exceptions after test failure

After a test has failed, test/py drains the U-Boot console log to ensure
that any relevant output is captured. At this point, we don't care about
detecting any additional errors, since the test is already known to have
failed, and U-Boot will be restarted. To ensure that the test cleanup code
is not interrupted, and can correctly terminate the log sections for the
failed test, ignore any exception that occurs while reading the U-Boot
console output during this limited period of time.

Signed-off-by: Stephen Warren <swarren@nvidia.com>