the-input-element/time.html: Use add_cleanup()

[cvrebert]

To ensure that failing tests don't interfere with other tests
Dangling min/max values were surviving after failed tests and interfering with later tests.
See also http://testthewebforward.org/docs/testharness-library.html#cleanup

[wpt-stability-bot]

Chrome (unstable channel)

Testing web-platform-tests at revision 1f3e68b
Using browser at version 55.0.2883.75
Starting 10 test iterations
All results were stable

All results

/html/semantics/forms/the-input-element/time.html

Subtest	Results
	OK
stepUp on step value zero	PASS
min attribute on default value check	PASS
step attribute on default value check	PASS
stepDown on step value 24 hour	PASS
stepDown on step value zero	PASS
stepUp on step value second	PASS
step attribute support on input element	PASS
stop at border on stepUp	FAIL
stepDown function support on input Element	PASS
type attribute support on input element	PASS
stepUp on step value 24 hour	PASS
set value on not time format value	PASS
stepDown on step value second	PASS
stepUp on step value hour	PASS
max attribute support on input element	PASS
empty value of stepUp	PASS
stepUp step value empty on default step value	PASS
min attribute support on input element	PASS
stepUp argment 2 times	PASS
stepDown on step value miri second	PASS
stepUp stop because it exceeds the maximum value	FAIL
stepUp on step value minus	PASS
max attribute on default value check	PASS
stepDown Stop so lower than the minimum value	FAIL
stepDown on step value hour	PASS
stepDown on step value minus	PASS
stepUp function support on input Element	PASS
stop at border on stepDown	PASS
time element of default time value	PASS
stepDown argment 2 times	PASS
stepDown step value empty default step value	PASS
stepUp on step value miri second	PASS

[wpt-stability-bot]

Firefox (nightly channel)

Testing web-platform-tests at revision 1f3e68b
Using browser at version BuildID 20170120225344; SourceStamp 3cedab21a7e65e6a1c4c2294ecfb5502575a46e3
Starting 10 test iterations
All results were stable

All results

/html/semantics/forms/the-input-element/time.html

Subtest	Results
	OK
stepUp on step value zero	PASS
min attribute on default value check	PASS
step attribute on default value check	PASS
stepDown on step value 24 hour	FAIL
stepDown on step value zero	PASS
stepUp on step value second	PASS
step attribute support on input element	PASS
stop at border on stepUp	FAIL
stepDown function support on input Element	PASS
type attribute support on input element	PASS
stepUp on step value 24 hour	PASS
set value on not time format value	PASS
stepDown on step value second	PASS
stepUp on step value hour	PASS
max attribute support on input element	PASS
empty value of stepUp	PASS
stepUp step value empty on default step value	PASS
min attribute support on input element	PASS
stepUp argment 2 times	PASS
stepDown on step value miri second	PASS
stepUp stop because it exceeds the maximum value	PASS
stepUp on step value minus	PASS
max attribute on default value check	PASS
stepDown Stop so lower than the minimum value	PASS
stepDown on step value hour	PASS
stepDown on step value minus	PASS
stepUp function support on input Element	PASS
stop at border on stepDown	PASS
time element of default time value	PASS
stepDown argment 2 times	PASS
stepDown step value empty default step value	PASS
stepUp on step value miri second	PASS

[jdm]

Thanks!