patches (commaai#582)

* selfdrive: add sys module to exit call

exit() is a helper for interactive shell. Let's explicit
use the module sys.

* selfdrive: tomstoned.py use constant for /data/tombstones/

Instead of use multiple times a string for
the data dir, use a variable.

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openpilot v0.5.9 release

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openpilot v0.5.7 release

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openpilot v0.5.6 release

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