build/vet: Fix all the shadowing reports with go1.6

Golang 1.6 is default version for the build now.

Additionally set 'GODEBUG=cgocheck=0' for now, until
we fix the erasure coding package.

Readmore here https://tip.golang.org/doc/go1.6#cgo

buildscripts/checkgopath.sh

@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+#
+# Minio Cloud Storage, (C) 2015, 2016 Minio, Inc.
+#
+# 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.
+#
+
+_init() {
+
+    shopt -s extglob
+
+    PWD=$(pwd)
+    GOPATH=$(go env GOPATH)
+}
+
+main() {
+    echo "Checking if project is at ${GOPATH}"
+    for minio in $(echo ${GOPATH} | tr ':' ' '); do
+        if [ ! -d ${minio}/src/github.com/minio/minio ]; then
+            echo "Project not found in ${minio}, please follow instructions provided at https://github.com/minio/minio/blob/master/CONTRIBUTING.md#setup-your-minio-github-repository" \
+                && exit 1
+        fi
+        if [ "x${minio}/src/github.com/minio/minio" != "x${PWD}" ]; then
+            echo "Build outside of ${minio}, two source checkouts found. Exiting." && exit 1
+        fi
+    done
+}
+
+_init && main
+