deleting server context wrappers in QPS test

Benchmark fixes

Delay beginning most writes until we enter poll()

This reveals an issue that needs to be solved:
D0713 14:48:28.049861213   14503 server.c:704]               Waiting for 44 channels and 0/1 listeners to be destroyed before shutting down server

Server was continuing to make requests for new calls forever, which were
starving out the shutdown sequence. Change order and win.

   These tests (especially unconstrained versions) can get very
   backlogged and may take a while to finish. We sometimes flake waiting
   for that. This is not hazardous (IMO), as the scripts that run these
   tests already have timeouts to make sure that these don't truly go on
   forever.

2. Make the time spent in the benchmark phase actually be
   benchmark_seconds rather than benchmark_seconds-warmup_seconds
   as it is currently.

since tsan slows things down a lot and may complicate issues such
as shutdown.

may cause inter-language confusion.

- make the directory structure match the package structure
- sanitize the package structure (test --> testing)
- add auto-detection of proto file dependencies

Make payloads respect the new defaults

Have not yet added tests with security support, coming soon

Remove some unused options and make server_threads relevant
Start stubbing out better qps/core calculations