Revert "test/time: no need to abs(uint64_t) for comparing"

Revert "test/time: no need to abs(uint64_t) for comparing"

This reverts commit da0f6608dd6cc3356e727e739575f496c2b6a590.

unittest_time fails:

[==========] Running 4 tests from 2 test cases.
[----------] Global test environment set-up.
[----------] 2 tests from RealClock
[ RUN      ] RealClock.Sanity
[       OK ] RealClock.Sanity (0 ms)
[ RUN      ] RealClock.Conversions
test/common/test_time.cc:125: Failure
Expected: ((Clock::from_double(bd) - brt).count()) < (30U), actual: 18446744073709551595 vs 30
[  FAILED  ] RealClock.Conversions (0 ms)
[----------] 2 tests from RealClock (0 ms total)

[----------] 2 tests from CoarseRealClock
[ RUN      ] CoarseRealClock.Sanity
[       OK ] CoarseRealClock.Sanity (0 ms)
[ RUN      ] CoarseRealClock.Conversions
test/common/test_time.cc:125: Failure
Expected: ((Clock::from_double(bd) - brt).count()) < (30U), actual: 18446744073709551595 vs 30
[  FAILED  ] CoarseRealClock.Conversions (0 ms)
[----------] 2 tests from CoarseRealClock (0 ms total)

[----------] Global test environment tear-down
[==========] 4 tests from 2 test cases ran. (0 ms total)
[  PASSED  ] 2 tests.
[  FAILED  ] 2 tests, listed below:
[  FAILED  ] RealClock.Conversions
[  FAILED  ] CoarseRealClock.Conversions

Signed-off-by: Sage Weil <sage@redhat.com>