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"
Skip to poll and publish when no resources found

Currently, the polling agent will poll and publish even if no resources
found. Although no samples will be published in publishing process, the
polling record will be recorded in log files, this is easy to mislead.
This change skip to publish and record a clear skip-polling hint in
log if no resources found.

Change-Id: Ia0294d3308a1d709006f9cb772f35ea92badcb38
Merge "Change event type for identity trust notifications"
Merge "Skip to poll and publish when no resources found"