Config variable to set locations to try for conftest.py files #430

Originally reported by: holger krekel (BitBucket: hpk42, GitHub: hpk42)

Discussed with @jurko and others: It would be good to have a conftestscan ini variable which you can set in order to have pytest scan for conftest files. Examples:

• conftestscan = test*/conftest.py (the default) would make pytest look for a conftest.py in any sub directory of the directory containing the ini-file.
• conftestscan = test*/**/conftest.py would make pytest do a recursive search in all subdirs.
• conftestscan = myproj/**/conftest.py would make pytest scan all subdirs in the project/package directory for conftest.py files.

Note that the only effect of conftestscan is to load conftest files early and make e.g. its command line options available. Any fixture functions or e.g. pytest_runtest_* hooks would still only be available to all the tests under the directory of the respective conftest.py file where they are defined. In other words, conftestscan does not turn conftest.py into global plugins.

• Bitbucket: https://bitbucket.org/pytest-dev/pytest/issue/430