lockfile: replace random() by rand()

lockfile: replace random() by rand()

On Windows, we do not have functions srandom() and random(). Use srand()
and rand(). These functions produce random numbers of lesser quality,
but for the purpose (a retry time-out) they are still good enough.

Signed-off-by: Johannes Sixt <redacted>
Reviewed-by: Michael Haggerty <redacted>
Signed-off-by: Junio C Hamano <redacted>