add event data to blacklist file
add event data to blacklist file

This makes the blacklist file a bit more verbose by including time of, and reason for,
blacklisting, which makes it easier to monitor device failures. Will later need to specify the
reason arg for everything that calls Extend().

Old format:
["serial1", "serial2"]

New format:
{
  "serial1": {"timestamp": 14444444444, "reason": "unauthorized"},
  "serial2": {"timestamp": 14444444444, "reason": "stupid_device"},
}

BUG=482259

Review URL: https://codereview.chromium.org/1406243005

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#356454}

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