t1400: set core.logAllRefUpdates in "logged by touch" tests

t1400: set core.logAllRefUpdates in "logged by touch" tests

A group of update-ref tests verifies that logs are created when either
the log file for the ref already exists or core.logAllRefUpdates is
"true".  However, when the default for core.logAllRefUpdates was
changed in 0bee59186 (Enable reflogs by default in any repository with
a working directory., 2006-12-14), the setup for the tests was not
updated.  As a result, the "logged by touch" tests would pass even if
the log file did not exist (i.e., if "--create-reflog" was removed
from the first "git update-ref" call).

Update the "logged by touch" tests to disable core.logAllRefUpdates
explicitly so that the behavior does not depend on the default value.
While we're here, update the "logged by config" tests to use
test_config() rather than setting core.logAllRefUpdates to "true"
outside of the tests.

Signed-off-by: Kyle Meyer <kyle@kyleam.com>
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>