Use k3sup to determine client arch

* Set image suffix for OpenFaaS

Signed-off-by: Alex Ellis (OpenFaaS Ltd) <alexellis2@gmail.com>

vendor/github.com/alexellis/k3sup/LICENSE

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+MIT License
+
+Copyright (c) 2019 Alex Ellis
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

vendor/github.com/alexellis/k3sup/pkg/env/env.go

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+package env
+
+import (
+	"log"
+	"strings"
+
+	execute "github.com/alexellis/go-execute/pkg/v1"
+)
+
+// GetClientArch returns a pair of arch and os
+func GetClientArch() (string, string) {
+	task := execute.ExecTask{Command: "uname", Args: []string{"-m"}}
+	res, err := task.Execute()
+	if err != nil {
+		log.Println(err)
+	}
+
+	arch := strings.TrimSpace(res.Stdout)
+
+	taskOS := execute.ExecTask{Command: "uname", Args: []string{"-s"}}
+	resOS, errOS := taskOS.Execute()
+	if errOS != nil {
+		log.Println(errOS)
+	}
+
+	os := strings.TrimSpace(resOS.Stdout)
+
+	return arch, os
+}