v0.11.1: External probe and stackdriver surfacer improvements

Enhancements

External probe

• Dynamic labels for the external probe metrics (#486). External probe programs can now add labels to payload-generated metrics by specifying labels in payload like this:

db_status{name=db01,region=us-west-2,status=running} 1.0
db_status{name=db02,region=us-east-1,status=running} 1.0

• Enhance payload parsing to support spaces in labels and string values (#491). Example:

version{service="service A",dc="xx"} "version 1.5.0"

Stackdriver surfacer

• Export unit for the "latency" metric (#349, #492). Not having unit for latency metric has been a constant source of confusion.
• Export "failure" metric along with the standard success, total and latency metrics. (#498).

Also added stackdriver surfacer documentation and an example.

Other enhancements

• Reliability and scalability improvement to GCE resources discovery: use per-scope caches (#479).
• OAuth: Check for ID token in OAuth token if access token is not set (#483).

Complete list of commits since the last release: v0.11.0...v0.11.1
Bugs/PR in this release: Milestone v0.11.1.