feat(agoric): make agoric --sdk install use yarn link

This makes it possible to have dapp package dependencies diverge
from agoric-sdk's.

packages/agoric-cli/lib/install.js

@@ -16,32 +16,57 @@ export default async function installMain(progname, rawArgs, powers, opts) {
   const subdirs = ['.', '_agstate/agoric-servers', 'contract', 'api'].sort();
 
   if (opts.sdk) {
-    const sdkNodeModules = path.resolve(__dirname, '../../../node_modules');
+    const sdkPackagesDir = path.resolve(__dirname, '../../../packages');
+    const allPackages = await fs.readdir(sdkPackagesDir);
+    const packages = new Map();
+    for (const pkg of allPackages) {
+      const dir = `${sdkPackagesDir}/${pkg}`;
+      let packageJSON;
+      try {
+        packageJSON = await fs.readFile(`${dir}/package.json`);
+      } catch (e) {
+        continue;
+      }
+      if (packageJSON) {
+        const pj = JSON.parse(packageJSON);
+        if (!pj.private) {
+          if (await pspawn('yarn', ['link'], { stdio: 'inherit', cwd: dir })) {
+            log.error('Cannot yarn link', dir);
+            return 1;
+          }
+          packages.set(pkg, pj.name);
+        }
+      }
+    }
     await Promise.all(
       subdirs.map(subdir => {
         const nm = `${subdir}/node_modules`;
         log(chalk.bold.green(`removing ${nm}`));
-        return rimraf(nm).then(_ => {
-          log(chalk.bold.green(`link SDK ${nm}`));
-          return fs.symlink(sdkNodeModules, nm);
-        });
+        return rimraf(nm);
       }),
     );
+    const sdkPackages = [...packages.values()].sort();
+    for (const subdir of subdirs) {
+      if (await pspawn('yarn', ['link', ...sdkPackages], { stdio: 'inherit', cwd: subdir })) {
+        log.error('Cannot yarn link', ...sdkPackages);
+        return 1;
+      }
+    }
   } else {
-    // Delete any symlinks.
+    // Delete all old node_modules.
     await Promise.all(
       subdirs.map(subdir => {
         const nm = `${subdir}/node_modules`;
         log(chalk.bold.green(`removing ${nm}`));
-        return fs.unlink(nm).catch(_ => {});
+        return rimraf(nm);
       }),
     );
+  }
 
-    if (await pspawn('yarn', ['install'], { stdio: 'inherit' })) {
-      // Try to install via Yarn.
-      log.error('Cannot yarn install');
-      return 1;
-    }
+  if (await pspawn('yarn', ['install'], { stdio: 'inherit' })) {
+    // Try to install via Yarn.
+    log.error('Cannot yarn install');
+    return 1;
   }
 
   if (await pspawn('yarn', ['install'], { stdio: 'inherit', cwd: 'ui' })) {