Fix timezones in line chart

Ceilometer gives us UTC and works with UTC, we should honor that
in line chart, cause we are just passing samples there.

Hover detail of sample should show localized time.

Change-Id: I83c23a13eb27b71e71268bc7b99c0ce0fdd1d59a
Closes-Bug: #1359690
(cherry picked from commit d787eb5e9a4dda7a2a6a493bebff166952ed2640)
Merge "Fix timezones in line chart" into stable/juno