storage/fs: change order of precedence for URL expansion

[sonmezonur]

• Glob(*) expansion must have precedence over directory expansion.

If the source URL is both glob and directory, s5cmd only copies objects in the directory. Example setup:

testdir
|-- abc*
|   |-- file1.txt
|   `-- file2.txt
`-- abcd
    |-- file1.txt
    `-- file2.txt

❯ s5cmd cp 'testdir/abc*' s3://bigtmp/prefix/
cp testdir/abc*/file2.txt s3://bigtmp/prefix/abc*/file2.txt
cp testdir/abc*/file1.txt s3://bigtmp/prefix/abc*/file1.txt

URL expansion for fs.List() is working like following:

1) if given source URL is a directory, it only walks the directory.
2) if given source URL has glob, it expands glob.
3) if given source is not glob or directory, it sends stat call to single file.

Since abc* is a directory, currently s5cmd does not try to expand glob. I think we should change the order of precedence for dir/glob expansion.

I added tests for both cp/rm commands.