Change the way kubectl-mongodb plugin is built by evergreen function

The evergreen function `build_multi_cluster_binary` is used to build the `kubectl-mongodb` plugin. And this function
gets used in the main `.evergreen.yml` file to build the `kubectl-mongodb` binary.
Since we moved the location of the source files for `kubectl-mongodb` plugin as part of [PR](#271),
this PR makes respective changes in the evergreen function so that it can properly build the `kubectl-mongodb` plugin from
the new location.

Author: viveksinghggits

scripts/evergreen/build_multi_cluster_kubeconfig_creator.sh

@@ -15,7 +15,7 @@ fi
 echo "Building multi cluster kube config creation tool."
 
 project_dir="$(pwd)"
-pushd public/tools/multicluster
+pushd cmd/kubectl-mongodb
 GOOS="${OS}" GOARCH="${ARCH}" CGO_ENABLED=0 go build -buildvcs=false -o "${project_dir}/docker/mongodb-kubernetes-tests/multi-cluster-kube-config-creator" main.go
 GOOS="linux" GOARCH="amd64" CGO_ENABLED=0 go build -buildvcs=false -o "${project_dir}/docker/mongodb-kubernetes-tests/multi-cluster-kube-config-creator_linux" main.go
 popd