Make initial connect retry backoff configurable

Upmerge from 1.0.x

Add method for creating insecure channel from FD with custom arguments using C++ API.

Clean up code

Remove completion queue parameter from `grpc_server_add_insecure_channel_from_fd` API

Use SIGMINRT + 6 as the default signal for gRPC epoll engine (instead of SIGMINRT + 2)

Move deadline functionality into filters.

Prevent nanopb fuzzers from spamming logs

Set initial backoff to 10000ms when creating channel in Objective C

Plugging memory leak.

Nanopb code drop

Improve gen_reflection_proto.sh

Set default max send message size to unlimited.

Add comments documenting ownership semantics

Remove unused files.

Rewrote handling of default resolver prefix

Changed deadline of internal LB channel.

Reduce load on Jenkins from running benchmarks as tests

Add a header to override grpc::string when needed

Prevent some compilers compaining unused return value