share: Presign objects under a dir prefix

[vadmeste]

From now on, when the user specifies to share a prefix which represents
a directory, all objects under that directory will be shared without
having to check for --recursive flag. If the latter is specified, all
objects in all subdirs will be shared.

Fixed #2204

[codecov-io]

Codecov Report

Merging #2215 into master will decrease coverage by <.01%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master   #2215      +/-   ##
=========================================
- Coverage    8.88%   8.87%   -0.01%     
=========================================
  Files          93      93              
  Lines        9028    9033       +5     
=========================================
  Hits          802     802              
- Misses       8099    8104       +5     
  Partials      127     127

Impacted Files	Coverage Δ
cmd/share-download-main.go	0% <0%> (ø)	⬆️

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[krisis]

@vadmeste, I have the following namespace,

➜  mc git:(r2215) mc ls -r s1/test
[2017-07-17 09:46:21 IST]   105B dir/obj1
[2017-07-17 09:46:21 IST]   105B dir/obj2
[2017-07-17 09:46:21 IST]   105B dir/obj3
[2017-07-17 09:46:21 IST]   105B dir/obj4
[2017-07-17 09:43:58 IST]   105B obj1
[2017-07-17 09:43:58 IST]   105B obj2
[2017-07-17 09:43:58 IST]   105B obj3
[2017-07-17 09:43:58 IST]   105B obj4

When I run mc share download s1/test/dir I don't see shared URLs of the objects under the prefix.
But when I run mc share download s1/test/dir/ I see share URLs of all the objects under the prefix.
This may be due to how we treat alias+path in mc, but this seems a little odd to me from a usability point of view. If we decide to stick to the current implementation we need to update mc-share's usage message.
I.e,

OPTIONS:
  --recursive, -r                  Share all objects recursively.

and

  4. Share all objects under this folder and all its sub-folders with 5 days expiry.
      $ mc share download --recursive --expire=120h s3/backup/

[vadmeste]

@krisis, I fixed the issue now. Thanks

[krisis]

@vadmeste The help message still needs to be changed.

[vadmeste]

@vadmeste The help message still needs to be changed.

There is nothing to update @krisis. --recursive will share all objects under the specified directory and its subdirs. Without --recursive, only objects directly located under the specified dir will be shared.

[vadmeste]

@krisis, help text updated. Please take a look again.