add a `strict` mode to readMetadata()

Test cases will set this to `false`, because they're
missing `scripts.start` and other required properties in this function

lib/read-metadata.js

@@ -16,6 +16,7 @@ module.exports = async function (path, {
   deploymentType = 'npm',
   deploymentName,
   quiet = false,
+  strict = true,
   isStatic = false
 }) {
   let pkg = {}
@@ -50,7 +51,7 @@ module.exports = async function (path, {
       }
     }
 
-    if (!pkg.scripts || (!pkg.scripts.start && !pkg.scripts['now-start'])) {
+    if (strict && (!pkg.scripts || (!pkg.scripts.start && !pkg.scripts['now-start']))) {
       const e = Error('Missing `start` (or `now-start`) script in `package.json`. ' +
         'See: https://docs.npmjs.com/cli/start.')
       e.userError = true
@@ -81,7 +82,7 @@ module.exports = async function (path, {
       throw e
     }
 
-    if (docker.length <= 0) {
+    if (strict && docker.length <= 0) {
       const e = Error('No commands found in `Dockerfile`')
       e.userError = true
       throw e