filer: support uploading file without needEnsureParentDir

[famosss]

Mostly,the parent dir has already exists or i can make the parent dir manually in advance.
Use the parameter,i can reduce one metadata request on per upload request.

[chrislusf]

This needEnsureParentDir is default to true, which is current behavior.

I am confused. Do you want to ensure parent directory or not? If so, it is already current behavior.

[famosss]

This needEnsureParentDir is default to true, which is current behavior.

I am confused. Do you want to ensure parent directory or not? If so, it is already current behavior.

By default,i want to ensure parent dir exists,It makes weedfs particularly easy to use.
But,I use curl -F file=@report.js "http://localhost:8888/javascript/some_file?ensureParentDir=false in my product environment to reduce the number of metadata requests.

In my case,I use BaikalDB to store the metadata, about 7ms to upload a file,but 3ms used to request the metadata service.The parameter can improve performance by about 14%(7ms -> 6ms)

[chrislusf]

Please do these:

• go fmt your changes.
• After the PR is merged, add to wiki about this API changes and what is the benefit, as you explained here. https://github.com/chrislusf/seaweedfs/wiki/Filer-Server-API

[famosss]

Please do these:

• go fmt your changes.
• After the PR is merged, add to wiki about this API changes and what is the benefit, as you explained here. https://github.com/chrislusf/seaweedfs/wiki/Filer-Server-API

done

[chrislusf]

I changed the code and doc to use skipCheckParentDir, which defaults to false.