Fix calls to rerequest

Use KeDiFa to store keys, and transmit the url to the requester for master
and slave partitions.

Download keys on the slave partitions level.

Tests are adapted to follow new way.

Improve tests.

TODO:

 * switch to SSL-only KeDiFa
 * awwait for KeDiFa SSL-auth and use it

With executing assertEqual(expected, given) the results, especially with
dicts or multiline strings, are more readable in case of failure.

Context, nicely filled in by slapos.recipe.template, is required in the macros.

Jerome Perrin:

Update stack/caucase/README.rst

Improves 57bdf689 by having stored and
expected values stable across runs.

Also assertion is done with {hash} instead its real value, as it has no
meaning to test user.

this is a followup of !427

/reviewed-on !431

Previously it was required to put \ into multi-entry gowork.install,
because the way it was processed was to directly pass it into bash
command, and if \n were there the command was cut by bash and the
trailing was considered as another command.

We can avoid that by explicitly processing \n in gowork.install and
translate it to just ' '. This helps people because now gowork.install
becomes just a regular multiline buildout entry, similar e.g. to
gowork.cpkgpath et all.

Here is one example where it helps:

jerome/slapos@95c45fe0 (comment 68408)

/reviewed-by @jerome
/reviewed-on nexedi/slapos!430

Since f427842b some software releases has been
found to be without pinnsed eggs for GitPython dependency.

/reviewed-on nexedi/slapos!432

/reviewed-on nexedi/slapos!427

/reviewed-on nexedi/slapos!413

using husky + lint-staged

There was two sections writing the file `bin/monitor-httpd` which led to some problems when running things

/reviewed-on nexedi/slapos!426

/reviewed-on nexedi/slapos!409

/reviewed-on nexedi/slapos!411

/reviewed-on nexedi/slapos!410

  Sticky computer on kvm cluster, will make the requester (root instance on this case), request
  the children on the same computer as itself.

/reviewed-on nexedi/slapos!421

usually, the software release path is :
in a web runner : /srv/slapgrid/slappartXX/srv/runner/project/buildout.cfg
in a test node : /srv/slapgrid/slappartX/srv/testnode/xx/inst/test0-XX/srv/runner/project/buldout.cfg

the previous regex was replacing in all slappartX and test0-X by the new test0-Y
which of course would make an existing path : /srv/slapgrid/test0-Y/.../test0-Y/...

This commit only replace the latest occurence in order to have
compatible code in the "normal" case, and in the test nodes