Relax some of the timing parameters in the Alarm unit tests

In certain environments (e.g., virtual machines), the alarm timeouts
can late by tens of ms (40ms have been observed in some cases).
Relaxing some of the unit tests timing parameters, so we can
continue testing for correctness as covered by the AlarmTest.

Bug: 28907913
Change-Id: I211c36a689774c5cdf427039e4c9184cf4147604