backport #7502 from dgquintas/cpp_compression_level

C++ Compression Level set properly

Ruby Tools: automatically include plugin argument in protoc command

PHP: cleanup for GA

PHP: use php7_wrapper to reduce duplicated codes on v1.0.x branch(final part)

Remove .rb suffix from grpc-tools scripts, to be consistent with other gems

Updated ruby protos to use new _pb filename

Avoid using certain C++11-isms with grpc::thread, as it's not necessarily std::thread.

PHP: add PHP7 to various Jenkins tests and update dockerfile

PHP: minor cleanup for GA v1.0 branch

PHP: use php7_wrapper to reduce duplicated codes on v1.0.x branch(second part)

PHP: use php7_wrapper to reduce dup-codes on v1.0.x branch

update copyright