Lamassu update script changes (#126)

* lamassu-migrate-config script added + lamassu-default.json

* lamassu update script changes

* lamassu-update unit test added

lib/options-loader.js

@@ -0,0 +1,46 @@
+const fs = require('fs')
+const path = require('path')
+const os = require('os')
+const argv = require('minimist')(process.argv.slice(2))
+
+/**
+ * @return {{path: string, opts: any}}
+ */
+function load () {
+  if (process.env.LAMASSU_CONFIG) {
+    const configPath = process.env.LAMASSU_CONFIG
+    return {
+      path: configPath,
+      opts: JSON.parse(fs.readFileSync(configPath))
+    }
+  }
+
+  if (argv.f) {
+    const configPath = argv.f
+    return {
+      path: configPath,
+      opts: JSON.parse(fs.readFileSync(configPath))
+    }
+  }
+
+  try {
+    const globalConfigPath = path.resolve('/etc', 'lamassu', 'lamassu.json')
+    return {
+      path: globalConfigPath,
+      opts: JSON.parse(fs.readFileSync(globalConfigPath))
+    }
+  } catch (_) {
+    try {
+      const homeConfigPath = path.resolve(os.homedir(), '.lamassu', 'lamassu.json')
+      return {
+        path: homeConfigPath,
+        opts: JSON.parse(fs.readFileSync(homeConfigPath))
+      }
+    } catch (_) {
+      console.error("Couldn't open lamassu.json config file.")
+      process.exit(1)
+    }
+  }
+}
+
+module.exports = load