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
Merge "Fix timezones in line chart"