Adds option to disable Stackdriver Export

[askmeegs]

Adds environment variable option to disable Stackdriver export for Metrics and Tracing, along with the option to turn off Stackdriver Profiler and Debugger.

All services still default to True for exporting to SD - must manually add the env variables to disable export.

Example deployment YAML:

        env:
        - name: PORT
          value: "7000"
        - name: DEBUGGER
          value: "False"
        - name: TRACE
          value: "False"
        - name: PROFILER
          value: "False"

shippingservice-d6567fcb7-9dg9z server {"message":"Debugger disabled.","severity":"info","timestamp":"2020-02-15T22:11:30.628788162Z"}
shippingservice-d6567fcb7-9dg9z server {"message":"Tracing disabled.","severity":"info","timestamp":"2020-02-15T22:11:30.628900674Z"}
shippingservice-d6567fcb7-9dg9z server {"message":"Stats disabled.","severity":"info","timestamp":"2020-02-15T22:11:30.629103694Z"}
shippingservice-d6567fcb7-9dg9z server {"message":"Shipping Service listening on port :50051","severity":"info","timestamp":"2020-02-15T22:11:30.629151017Z"}

[daniel-sanche]

LGTM. I deployed to a fresh cluster and had no issues

[ahmetb]

I think my main feedback would be: Do not parse booleans.
YAML especially is notoriously bad for storing booleans.

Instead of doing TRACE="False", consider checking for existence of a flag, for example DISABLE_TRACE, and any value that's set (even 0) would just disable it.

[ahmetb]

^ This alone would simplify a lot of the current code.

[askmeegs]

@ahmetb does this look ok to merge?

[ahmetb]

Couple nits, otherwise looking good.