tst: Add test for utime

This patch provides test for utime. It uses wrapper to read access
and modification times to compare them with ones written by utime.

Moreover, access and modification times beyond the Y2038 threshold
date (i.e. 32 bit time_t overflow) are also checked.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>