Merge branch 'master' of github.com:grpc/grpc into gcc6

BUILD

Makefile

binding.gyp

build.yaml

config.m4

gRPC.podspec

grpc.def

grpc.gemspec

include/grpc++/security/server_credentials.h

include/grpc/grpc_security.h

include/grpc/grpc_security_constants.h

package.xml

src/boringssl/err_data.c

src/core/ext/lb_policy/pick_first/pick_first.c

src/core/lib/security/credentials.c

src/core/lib/security/security_connector.c

src/core/lib/security/security_connector.h

src/core/lib/tsi/ssl_transport_security.c

src/core/lib/tsi/ssl_transport_security.h

src/core/lib/tsi/transport_security_interface.h