If slapos.libnetworkache is not available, setup environment in no-op way.

Keep same ordering and simplify conditions.

If it is possible to use slapos.libnetworkcache check if parameter
networkcache-section exists. If so, try to find section named by this parameter.

Such section has two required parameters: download-cache-url and
download-dir-url. upload-cache-url and upload-dir-url are optional parameters.

Minimalistic profile for networkcache control looks like:

  [buildout]
  parts =

  networkcache-section = readcache

  [readcache]
  download-cache-url = http:///
  download-dir-url = http:///
  #upload-cache-url = http:///
  #upload-dir-url = http:///

This reverts commit da697e8e.

This commit does not seems required.

the behavior still the same.

So, a new method has been implemented in order to define the directory
key for each file which the buildout must download.

Removed useless method which should not exist.

After this commit it is possible to download and upload anything to
SHACACHE and SHADIR servers.

It uses slapos.libnetworkcache to handle the download and upload.

Copy and paste mistake.

It has been moved to slapos.tool.libnetworkcache.