use randomString/Number from lib in api tests (#2542)

test/automated/api/lib/rand.js

@@ -0,0 +1,16 @@
+const crypto = require('crypto');
+const Random = require('crypto-random');
+
+//returns a random number in range of [1 - max]
+function randomNumber(max = 5) {
+	return Random.range(1, max);
+}
+
+//returns a random hex string
+function randomString(length = 20) {
+    const bytesCount = Math.ceil(length / 2);
+    return crypto.randomBytes(bytesCount).toString('hex').substring(0, length);
+}
+
+module.exports.randomNumber = randomNumber;
+module.exports.randomString = randomString;