I put these in while debugging correctness, and forgot to remove them.

Make debugging a little easier, and remove an unnecessary assert

The mappings are a combination of useless, inaccurate, and harmful.
Leave them out until they are helpful and correct.

Fundamental issues:
 - If in need of mappings, a user would need HTTP -> gRPC code mappings.
   But the docs don't provide that since the mappings are not 1:1.
 - There _is no_ gRPC -> HTTP code mapping taking place in gRPC. This
   may change in the future, but until then the docs are misleading.

But even given those were resolved, there are additional issues. Two
obvious examples:
 - 501 Not Implemented is refering to HTTP methods such as GET and POST
   not being implement. That should not be used for gRPC methods not
   found (UNIMPLEMENTED).
 - 404 Not Found is for when the resource is not found. In gRPC, the
   resource is the gRPC method, not the parameters (NOT_FOUND). If there
   is a REST conversion layer on top of gRPC, then 404 would be
   appropriate, but that just shows that the mapping can not be
   canonical.

With this change the Python code generated by the Python code generator
uses the grpc.early_adopter package and not the grpc.framework.face
package.

First: ugh.

Second: allow tracer global variables to be registered and then parsed out of a configuration environment variable.

Expose TSI trace config variable directly to ease this a little.

This allows for easier scripting and updates.

size error

Fix pedantic warnings of form:

   myprotobuf.pb.cc:619:2: warning: extra ';' [-Wpedantic]
    };
     ^

bind and other functions

Fixes module path finding in the Python code generator and the signatures
of generated servicer methods.

The server_host_override flag's implementation remaining
outstanding means that this only works over insecure
connections for now.