test: Add testutil.HttpServer

The goal is to remove supertest as it does not support typescript well
and there's really no good reason for the dependency. Also no websocket
testing support.

package.json

@@ -38,13 +38,13 @@
     "@types/js-yaml": "^3.12.3",
     "@types/mocha": "^8.0.3",
     "@types/node": "^12.12.7",
+    "@types/node-fetch": "^2.5.7",
     "@types/parcel-bundler": "^1.12.1",
     "@types/pem": "^1.9.5",
     "@types/proxy-from-env": "^1.0.1",
     "@types/safe-compare": "^1.1.0",
     "@types/semver": "^7.1.0",
     "@types/split2": "^2.1.6",
-    "@types/supertest": "^2.0.10",
     "@types/tar-fs": "^2.0.0",
     "@types/tar-stream": "^2.1.0",
     "@types/ws": "^7.2.6",
@@ -61,7 +61,6 @@
     "prettier": "^2.0.5",
     "stylelint": "^13.0.0",
     "stylelint-config-recommended": "^3.0.0",
-    "supertest": "^6.0.1",
     "ts-node": "^9.0.0",
     "typescript": "4.0.2"
   },
@@ -81,6 +80,7 @@
     "httpolyglot": "^0.1.2",
     "js-yaml": "^3.13.1",
     "limiter": "^1.1.5",
+    "node-fetch": "^2.6.1",
     "pem": "^1.14.2",
     "proxy-agent": "^4.0.0",
     "proxy-from-env": "^1.1.0",