RFR: 327: git webrev: Print the location of the generated webrev upon successful completion

[Zhao Song]

Originally, git webrev command would return nothing when executed successfully. It is not a good experience for user. 

Right now, when executed successfully, the location of index.html will be printed.

Also, added a --quiet flag if the current silent behavior is required.

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Commit messages:
 - print webrev location after 'git webrev' execute successfullu

Changes: https://git.openjdk.org/skara/pull/1379/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1379&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-327
  Stats: 9 lines in 1 file changed: 8 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/skara/pull/1379.diff
  Fetch: git fetch https://git.openjdk.org/skara pull/1379/head:pull/1379

PR: https://git.openjdk.org/skara/pull/1379