Pin versions on unstable packages: grpc-core internal and netty

The internal package is very unstable, so any users of it are not
compatible with alternative versions of grpc-core. The same is true for
HTTP/2 support in Netty. This primarily helps Maven users; Gradle
appears to ignore the distinction between '$version' and '[$version]'
and does not trigger a build failure.

Projects like grpc-stub don't depend on internal, so they aren't using
the version pinning. The whitelist is a bit prone to go out-of-date, but
introducing grpc-api would be the long-term solution.

Fixes #1459

build.gradle

@@ -137,7 +137,7 @@ subprojects {
  protobuf_plugin: 'com.google.protobuf:protobuf-gradle-plugin:0.7.4',
  protobuf_util: "com.google.protobuf:protobuf-java-util:${protobufVersion}",
 
- netty: 'io.netty:netty-codec-http2:4.1.0.CR6',
+ netty: 'io.netty:netty-codec-http2:[4.1.0.CR6]',
  netty_epoll: 'io.netty:netty-transport-native-epoll:4.1.0.CR6' + epoll_suffix,
  netty_tcnative: 'io.netty:netty-tcnative-boringssl-static:1.1.33.Fork15:' + osdetector.classifier,
 
@@ -272,6 +272,14 @@ subprojects {
  }
  }
  }
+ if (!(project.name in
+ ["grpc-stub", "grpc-protobuf", "grpc-protobuf-lite", "grpc-protobuf-nano"])) {
+ def core = pom.dependencies.find {dep -> dep.artifactId == 'grpc-core'}
+ if (core != null) {
+ // Depend on specific version of grpc-core because internal package is unstable
+ core.version = "[" + core.version + "]"
+ }
+ }
  }
  // At a test failure, log the stack trace to the console so that we don't
  // have to open the HTML in a browser.