SPARK-1812: use consistent protobuf version across build

Moving to akka-2.3 reveals issues where differing protobuf
versions within the same build results in runtime incompatibility
and exceptions like:

  java.lang.VerifyError: class akka.remote.WireFormats$AkkaControlMessage overrides final method getUnknownFields.()Lcom/google/protobuf/UnknownFieldSet;
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:800)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
    at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)

Signed-off-by: Anand Avati <avati@redhat.com>
SPARK-1812: core - upgrade to akka 2.3.4

Signed-off-by: Anand Avati <avati@redhat.com>
SPARK-1812: streaming - remove tests which depend on akka.actor.IO

Not available in 2.3.x

Signed-off-by: Anand Avati <avati@redhat.com>
SPARK-1812: tools - fix scalastyle error

error file=spark/tools/src/main/scala/org/apache/spark/tools/GenerateMIMAIgnore.scala message=File line length exceeds 100 characters line=118

Signed-off-by: Anand Avati <avati@redhat.com>