[VOL-2193] Create mocks for Kafka Client and Etcd

This commit consists of:
1) A kafka client mock that implements the kafka client interface
under voltha-lib-go/pkg/kafka/client.go
2) An embedded Etcd server that runs in-process and represents an
Etcd server.

Change-Id: I52a36132568e08c596bb4136918bebcb654a3b99
diff --git a/vendor/github.com/prometheus/procfs/Makefile b/vendor/github.com/prometheus/procfs/Makefile
new file mode 100644
index 0000000..616a0d2
--- /dev/null
+++ b/vendor/github.com/prometheus/procfs/Makefile
@@ -0,0 +1,29 @@
+# Copyright 2018 The Prometheus Authors
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+include Makefile.common
+
+%/.unpacked: %.ttar
+	@echo ">> extracting fixtures"
+	./ttar -C $(dir $*) -x -f $*.ttar
+	touch $@
+
+update_fixtures:
+	rm -vf fixtures/.unpacked
+	./ttar -c -f fixtures.ttar fixtures/
+
+.PHONY: build
+build:
+
+.PHONY: test
+test: fixtures/.unpacked common-test