dev-db/etcdctl: add etcdctl v3 package

This complements dev-db/etcd with USE="-etcdctl"

See https://github.com/coreos/bugs/issues/1717 for the motivation for
providing etcdctl as a separate package with a newer version.

sdk_container/src/third_party/coreos-overlay/dev-db/etcdctl/Manifest

@@ -0,0 +1 @@
+DIST etcdctl-3.2.6.tar.gz 2886557 SHA256 23ab4016bf0a057d36461cee001dc5b38d0d757fa5d9e8226833687dab06faa2 SHA512 3e26bc12cafbead201b41d7f25e247f24b3480ebcc76e94f2ae4e12e573a973b60e28f36fa012d1f7bc21edc670fd8910b33cd7e9f30c3a809a6f186af3ffc9d WHIRLPOOL 203833459801b18bd000bc1420f3ab14a7de601b3c18798c2537b75a510e720e5408424388bb7d643014a0de9870213533661bfad487ae30846969fdfa8efdf8

sdk_container/src/third_party/coreos-overlay/dev-db/etcdctl/etcdctl-3.2.6.ebuild

@@ -0,0 +1,31 @@
+# Copyright 1999-2017 Gentoo Foundation
+# Distributed under the terms of the GNU General Public License v2
+
+EAPI=5
+
+EGO_PN="github.com/coreos/etcd"
+COREOS_GO_PACKAGE="${EGO_PN}"
+DESCRIPTION="The etcd command line client, v3, compatible with v2"
+HOMEPAGE="https://github.com/coreos/etcd"
+SRC_URI="https://${EGO_PN}/archive/v${PV}.tar.gz -> ${P}.tar.gz"
+
+inherit coreos-go golang-vcs-snapshot
+COREOS_GO_VERSION="go1.8"
+
+LICENSE="Apache-2.0"
+SLOT="0"
+KEYWORDS="amd64 arm64"
+IUSE=""
+
+S=${WORKDIR}/${P}/src/${EGO_PN}
+
+DEPEND=""
+RDEPEND="${DEPEND}"
+
+src_compile() {
+	go_build "${COREOS_GO_PACKAGE}/cmd/etcdctl"
+}
+
+src_install() {
+	dobin ${WORKDIR}/gopath/bin/etcdctl
+}