* fn: mutex while waiting I/O considered harmful
*) Removed hold mutex while wait I/O cases these
included possible disk I/O and network I/O.
*) Error/Context Close/Shutdown semantics changed since
the context timeout and comments were misleading. Close
always waits for pending gRPC session to complete.
Context usage here was merely 'wait up to x secs to
report an error' which only logs the error anyway.
Instead, the runner can log the error. And context
still can be passed around perhaps for future opencensus
instrumentation.
* support runner TLS certificates with specified certificate Common Names
* removes duplicate constant
* run in insecure mode by default but expose ability to create tls-secured runner pools programmatically
* fixes runner tests to use new tls interfaces
* Move out node-pool manager and replace it with RunnerPool extension
* adds extension points for runner pools in load-balanced mode
* adds error to return values in RunnerPool and Runner interfaces
* Implements runner pool contract with context-aware shutdown
* fixes issue with range
* fixes tests to use runner abstraction
* adds empty test file as a workaround for build requiring go source files in top-level package
* removes flappy timeout test
* update docs to reflect runner pool setup
* refactors system tests to use runner abstraction
* removes poolmanager
* moves runner interfaces from models to api/runnerpool package
* Adds a second runner to pool docs example
* explicitly check for request spillover to second runner in test
* moves runner pool package name for system tests
* renames runner pool pointer variable for consistency
* pass model json to runner
* automatically cast to http.ResponseWriter in load-balanced call case
* allow overriding of server RunnerPool via a programmatic ServerOption
* fixes return type of ResponseWriter in test
* move Placer interface to runnerpool package
* moves hash-based placer out of open source project
* removes siphash from Gopkg.lock
