Revert "Prefer ANDROID_ALARM_ELAPSED_REALTIME over CLOCK_MONOTONIC"

This reverts commit d17647c3fd255182933148ce74389a5584ee5189.
[iphb] Prefer CLOCK_BOOTTIME over CLOCK_MONOTONIC

The CLOCK_MONOTONIC might get frozen during suspend.
CLOCK_BOOTTIME does not have this problem and should be used
when available.
Merge pull request #38 from pgerdt/clock_boottime

[iphb] Prefer CLOCK_BOOTTIME over CLOCK_MONOTONIC