add --override-ini option to overrides ini values

Signed-off-by: Ted Xiao <xiao.xj@gmail.com>

_pytest/helpconfig.py

@@ -20,6 +20,10 @@ def pytest_addoption(parser):
     group.addoption('--debug',
                action="store_true", dest="debug", default=False,
                help="store internal tracing debug information in 'pytestdebug.log'.")
+    # support for "--overwrite-ini ININAME=INIVALUE" to override values from the ini file
+    # Example '-o xfail_strict=True'.
+    group._addoption('-o', '--override-ini', nargs='*', dest="override_ini", action="append",
+               help="overrides ini values which do not have a separate command-line flag")
 
 
 @pytest.hookimpl(hookwrapper=True)