Use elapsed time not wall time for alarms so users can't play with the
system time to get around things.
Also using NTP servers to pull in an authoritative time - if we the build
is configured with an NTP server we will not advance to the next cycle
without it, but we also will not trottle - rather not throttle users
on an error.
Note that the poll alarm is just relative to the last poll time and real
time doesn't matter.
Defining the time-fetching API's as returning time in the system wallclock
range (correcting if we are using NTP time internally).
bug:2597530
Change-Id: I1c0ac0923314c2f8a04edd0b36c4845352eae99a
7171ea8179