tests: introduce RCM API testing executable

It is an equivalent to what we already have for Weldr API but this one
is for the RCM API. It should test the expected use cases:
 * submit a compose
 * get a status

cmd/osbuild-rcm-tests/main.go

@@ -0,0 +1,42 @@
+// osbuild-rcm-tests run tests against running osbuild-composer instance that was spawned using the
+// osbuild-rcm.socket unit. It defines the expected use cases of the RCM API.
+package main
+
+import (
+	"bytes"
+	"log"
+	"net/http"
+	"os"
+	"strings"
+)
+
+func main() {
+	failed := false
+	submit_body := `
+		{
+			"distribution": "fedora-31",
+		 	"image_types": ["qcow2"], 
+ 		 	"architectures":["x86_64"], 
+			"repositories": [
+				{"url": "http://download.fedoraproject.org/pub/fedora/linux/releases/30/Everything/x86_64/os/"}
+			]
+		}
+	`
+	socket := "http://127.0.0.1:80/"
+	endpoint := "v1/compose"
+	resp, err := http.Post(socket + endpoint, "application/json", strings.NewReader(submit_body))
+	if err != nil {
+		log.Fatal("Failed to submit a compose")
+	}
+	if resp.StatusCode != 200 {
+		log.Print("Error: the ", endpoint, " returned non 200 status. Full response: ", resp)
+		failed = true
+	} else {
+		buf := new(bytes.Buffer)
+		_, _ = buf.ReadFrom(resp.Body)
+		log.Print("Success: the ", endpoint, " returned: ", buf.String())
+	}
+	if failed {
+		os.Exit(1)
+	}
+}