flash: Provide clear progress feedback

- Provide clearer progress feedback at the default logging level
- Previously there was only a single log during the flash process
  that said "Update completed", however that happened less than
  halfway through the process and is misleading.
- This promotes a couple of INFO logs to NOTICE to mark the major
  phases of the flash process.
- Adds a new NOTICE to mark the payload staging phase.
- Downgrades some NOTICE's to INFO's that are ambiguous.
- This CL only changes logging.
- See also go/cros-flash-vs-wfh

BUG=chromium:1034015
TEST=manual

Change-Id: Ie783b63b883b6238110ce37cdbae84c98be5988b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2220400
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Tested-by: Zentaro Kavanagh <zentaro@chromium.org>
Commit-Queue: Amin Hassani <ahassani@chromium.org>
diff --git a/cli/flash.py b/cli/flash.py
index 6f80d7a..13fe016 100644
--- a/cli/flash.py
+++ b/cli/flash.py
@@ -509,6 +509,7 @@
 
         try:
           # Get payload directory
+          logging.notice('Staging payloads...')
           payload_dir = self.GetPayloadDir(device)
 
           # Do auto-update