Enable discovery of log_handler tests.

[robertwb]

Also fix the one remaining bug.

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[robertwb]

R: @herohde @kennknowles

[kennknowles]

LGTM

[herohde]

LGTM

[coveralls]

Changes Unknown when pulling 566d6e1 on robertwb:yet-more-grpc-fixes into ** on apache:master**.

[asfgit]

SUCCESS

--none--