Log exceptions in test_environment
Log exceptions in test_environment

Log full exception messages with traces when trying to kill web servers and
enable root on devices.

BUG=

Review URL: https://codereview.chromium.org/1294323002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#344221}

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