Add encoding to keys in compute_signature

Unlike fixed sample keys as counter_name and counter_volume,
metadata keys may contain unicode characters.
ceilometer.publisher.utils.compute_signature can't calculate
signature of unicode symbols and crashes.
In this patch encoding keys is added.

Change-Id: I94d02ce20999510e9c6aaf33f7ee503bbb350e87
Closes-bug: #1391517
Change event type for identity trust notifications

Our identity trust notification event type do not match keystone
event type for these notifications. This patch fix it.

Change-Id: I73c4ce9334a26574f3b2c83244ea67b219bec920
Closes-bug: #1392326
Merge "Add encoding to keys in compute_signature"
Merge "Change event type for identity trust notifications"