Exceptions occurring during check executions are not formatted - so not easily readable

[vetinari]

With the merge of zalando-zmon/zmon-worker#310 we get a stack trace in the "value" field of a check like

"Traceback (most recent call last):\n  File \"/usr/local/lib/python2.7/dist-packages/zmon_worker-0.1-py2.7.egg/zmon_worker_monitor/zmon_worker/tasks/main.py\", line 1200, in _get_check_result_internal\n    result = safe_eval(cmd, eval_source='<check-command>', **ctx)\n  File \"/usr/local/lib/python2.7/dist-packages/zmon_worker-0.1-py2.7.egg/zmon_worker_monitor/zmon_worker/common/eval.py\", line 187, in safe_eval\n    return c()  # if a function will return another callable, we will not call it\n  File \"<check-command>\", line 3, in check\nKeyError: 'foo'\n"

This should be formatted nicely, so it's readable and not just one long line.

The stack trace above was created by running

def check():
    foo = {'bar': 'baz'}
    return foo['foo']

in trial run

[vetinari]

For exceptions in the alert it's in captures['exception']

[beverage]

@vetinari We cannot repro this - is it still an issue?

[beverage]

Example:

https://zmon.zalando.net/#/trial-run?json=%7B%22entities%22:%5B%7B%22type%22:%22local%22,%22infrastructure_account%22:%22aws:<aws_account_id>%22%7D%5D,%22entities_exclude%22:%5B%5D,%22parameters%22:%7B%7D,%22interval%22:120,%22name%22:%22foo%22,%22description%22:%22bar%22,%22owning_team%22:%22Eagle%20Eye%22,%22check_command%22:%22def%20check():%5Cn%20%20%20%20return%205%2F0%22,%22alert_condition%22:%22True%22%7D

[arajain]

Fixed