Minor improvements on bugreport generation.

- Skipped artificial 100/100 message, since pulling will take care of
  the final 100% progress.
- Consolidated unsupported lines in just one message.
- Let user know the bugreport can still be recovered when it could not
  be copied to the destination directory.

BUG: 30451114

Change-Id: Icfce9c1e8e7ed407719728b9874679ac40b21eab
(cherry picked from commit 80a65d03)