Add support to propagate ONOS log to Kafka with KafkaAppender in log4j2

- new OSGi Bundle to define extra imports for log4j2
- update OSGiWrapper to support fragment-host tag + bugfix
- add kafka-clients to onos-dependencies package
- add example of how to propagate log to Kafka via KafkaAppender
- bugfix to org.ops4j.pax.logging.cfg

Change-Id: I89992936101a48c6452082bf23c7133c20aa0b48
diff --git a/tools/build/bazel/osgi_java_library.bzl b/tools/build/bazel/osgi_java_library.bzl
index 0ca2047..491444f 100644
--- a/tools/build/bazel/osgi_java_library.bzl
+++ b/tools/build/bazel/osgi_java_library.bzl
@@ -85,6 +85,7 @@
     web_xml = ctx.attr.web_xml
     dynamicimportPackages = ""
     karaf_commands = ctx.attr.karaf_commands
+    fragment_host = ctx.attr.fragment_host
     cp = ""
 
     inputDependencies = [input_file]
@@ -122,6 +123,7 @@
         "classes",
         bundle_classpath,
         karaf_commands,
+        fragment_host,
     ]
 
     ctx.actions.run(
@@ -155,6 +157,7 @@
         "web_xml": attr.label_list(allow_files = True),
         "include_resources": attr.string(),
         "karaf_commands": attr.string(),
+        "fragment_host": attr.string(),
         "_bnd_exe": attr.label(
             executable = True,
             cfg = "host",
@@ -366,7 +369,8 @@
         group = "org.onosproject",
         import_packages = "*",
         visibility = ["//visibility:private"],
-        generate_pom = False):
+        generate_pom = False,
+        fragment_host = ""):
     _bnd(
         name = name,
         source = jar,
@@ -376,6 +380,7 @@
         visibility = visibility,
         import_packages = import_packages,
         web_xml = None,
+        fragment_host = fragment_host,
     )
 
     if generate_pom: