Instead use provided system level tools to generate keys.

This reverts commit bfe5fb83.

After merging the master branch inside the signature branch of
slapos.libnetworkcache it is required to fix some error messages.

Thanks to 4784a35e, which does buildout
"patching" procedure in test it is not required to provide testnc.

By the way revert "Revert "Revert "Allow to find slapos.libnetworkcache during
test.""" (commit 0fbf2ccf ), as it is not
required anymore.

Whenever special sign ? is found in url analyse it in order to have
correct filename.

In case of http://host/path/filename/? use "filename" as part to
generate filename.

This fuzzy logic allows to generate quite sane filenames.

The changes were made in the previous commit:
 - 75a7c904

We should only create the signature files when it is required, to avoid
to have unecessary failures if someone run this test with old version of
slapos.libnetworkcache.

This reverts commit 01b2ca0a.

The slapos.libnetworkcache == 0.2 does not provide the signature script.

So, it should not be used if such script is not available.

Well, the new version of slapos.libnetworkcache has being developed,
and we need to provided backward compatibility to the old versions.

So, slapos.buildout must be able to instantiate a NetworkcacheClient
object even if an TypeError is raised.

As slapos.libnetworkcache development shall be outside on buildout, do not
create hard dependency.

This reverts commit 4dc2aef8.

For now this is the only working way to test buildout with
slapos.libnetworkcache.

slapos.libnetworkcache development shall be NOT zc.buildout driven.

This reverts commit e3345a7a.

Doing development of zc.buildout parts which shall depend on
slapos.libnetworkcache without ability to develop it locally is nowhere path.

This reverts commit bacd2505.

Doing development without local slapos.libnetworkcache has no sense.

By having newline in interpreter name, z3c.recipe.scripts created
bin/\npync file, and such was returned. This lead to returning
buildout:bin-directory path, which was killing buildout in next run.

As described the previous commit:
 - 5a5bff2f

We must use this method to create the required files to test if the
signature is working as expected.

So, first we create the files...

It must be possible to append information on shadir files, it must
simulate the real server. Otherwise there is no way to test the behavior
using different signatures.

This method is a wrapper to the signature script which is available at
slapos.libnetworkcache.git.

We should provide this method to be able to create the files required
during the test of signature feature on network.txt doctest.

This reverts commit b6730a8b.

Well, according to this commit at slapos.core.git:
  - 017a02ef202b69dff03e85de18293bc30ac6b545

This parameter is always under networkcache section to keep the
configuration consistenty.

Well, according to the commit d8dca883a54ee87aafed3a82921594e5b508b388
at slapos.core.git, this parameter is always under networkcache section
to keep the configuration consistenty.

Renamed signature_private_file to signature_private_key_file.
And also signature_public_file to signature_certificate_file.

Both files must be generated by opensssl.
- signature_public_file: used to verify if the content is trustable by
  libnetworkcache
- signature_private_file: used to generate the signature before uploading
  the content to shadir by libnetworkcache.

As networkcache is really optional, silence it in case if not enabled nor not
availble.