Add meta files to crash directory, enabling OS version at crash time.

Adding meta files also:
1) ensures atomically added crash reports
2) allows us to remove orphaned crash report payload files
   (such as core files)
3) gives us better control over the number of reports in
   crash directory

While we're here, also made these minor changes
1) send board (x86-generic, x86-mario, etc) to crash server
2) send hwclass to crash server
3) Only record crash reports when metrics are enabled.
4) No longer allow crash reporting to staging server.

TEST=unit tests plus UserCrash,CrashSender,KernelCrash autotests

Change-Id: Ieea9bdc8e0680b379c65b91cc56ca0611dd0f31c

Review URL:
9 files changed
tree: 89b7a4a468b50734913ac399c2d7842fe28b222e
  1. crash_reporter/