Zen: Update condition text for current condition.

If the provider sends us an updated summary (or other text)
for the currently selected exit condition, update the UI and
persisted condition.

Update the downtime condition text (end time/line2 + summary)
when the next alarm changes (if downtime = none).

Also, clear the fired-alarm cache on time or time-zone resets.

Bug: 16373455
Change-Id: Ib38c52104a281fcc04a89612b643a219fd82b40b