tests running with MySQL backend produces suspicious warnings

This ticket is a migrated Trac ticket [3451](http://trac.buildbot.net/ticket/3451)

People contributed to the original ticket: @rutsky
Ticket created on: `Feb 13 2016`
Ticket last modified on: `Feb 23 2016`

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E.g. [[these one|https://travis-ci.org/buildbot/buildbot/jobs/108976653]]:

Warning: BLOB/TEXT column 'state_string' can't have a default value

In my env I also seen this warning:

Warning: Invalid utf8 character string: 'FFFF00'

This issue should be investigated.

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_Comment from_: @rutsky
_Date_: `Feb 23 2016`

In https://github.com/buildbot/buildbot/pull/2015 @Riziero provides workaround for `can't have a default value` warnings, by setting `sql_mode='MYSQL40'` in MySQL configuration.
Is this a "true way" to solve this issue?

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_Comment from_: @rutsky
_Date_: `Feb 23 2016`

Looks like `can't have a default value` is warning on Linux and fatal error on Windows: http://stackoverflow.com/a/4553664/391865