Bug fixes in zc.buildout.testing

================================

Logging handler which did not get deleted

-----------------------------------------

The buildout testing set up runs a buildout which adds a

``logging.StreamHandler`` to the root logger. But tear down did not

remove it. This can disturb other tests of packages reusing

zc.buildout.testing.

The handers before calling set up are:

    >>> import logging

    >>> len(logging.getLogger().handlers)

    1

    >>> logging.getLogger().handlers # doctest: +ELLIPSIS

    [<zope...testrunner.logsupport.NullHandler instance at ...>]

After calling it, a ``logging.StreamHandler`` was added:

    >>> import zc.buildout.testing

    >>> import doctest

    >>> test = doctest.DocTestParser().get_doctest(

    ...     '>>> x', {}, 'foo', 'foo.py', 0)

    >>> zc.buildout.testing.buildoutSetUp(test)

    >>> len(logging.getLogger().handlers)

    2

    >>> logging.getLogger().handlers # doctest: +ELLIPSIS +NORMALIZE_WHITESPACE

    [<zope...testrunner.logsupport.NullHandler instance at ...>,

     <logging.StreamHandler instance at ...>]

But tear down removes the new logging handler:

    >>> zc.buildout.testing.buildoutTearDown(test)

    >>> len(logging.getLogger().handlers)

    1

    >>> logging.getLogger().handlers # doctest: +ELLIPSIS

    [<zope...testrunner.logsupport.NullHandler instance at ...>]