[Buildbot] #3446: add tests configuration that uses persistent SQLite database

[Buildbot trac]

#3446: add tests configuration that uses persistent SQLite database
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Reporter:  rutsky     |       Owner:
    Type:  undecided  |      Status:  new
Priority:  major      |   Milestone:  0.9.+
 Version:  master     |  Resolution:
Keywords:             |
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Comment (by rutsky):

 Also docs should be updated to include example of file-based SQLite:
 https://github.com/buildbot/buildbot/blame/master/master/docs/developer/database.rst#L1859

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Ticket URL: <http://trac.buildbot.net/ticket/3446#comment:1>
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