[Snapshot Restore] Increase sleep time in snapshot restore test (elas…

…tic#171218)

## Summary

While running the Snapshot restore test locally, I noticed that
sometimes it fails because the created test snapshot is still loading at
the time when the web driver tries to click the "Restore" button, so I'm
increasing the sleep time a bit to make sure we allow enough time for
the snapshot to be ready and to future-proof the test against flakiness.

Flaky test runner build:
https://buildkite.com/elastic/kibana-flaky-test-suite-runner/builds/3982

x-pack/test/functional/apps/snapshot_restore/snapshot_restore.ts

@@ -38,7 +38,7 @@ export default ({ getPageObjects, getService }: FtrProviderContext) => {
       });
 
       // Wait for snapshot to be ready
-      await pageObjects.common.sleep(1000);
+      await pageObjects.common.sleep(2000);
 
       // Refresh page so that the snapshot shows up in the snapshots table
       await browser.refresh();