Query the API to find the latest Debian image to deploy the base system with.

* gnu/machine/hetzner/http.scm (null-or): New procedure.
(<hetzner-image>): New JSON record type.
(<hetzner-image-created-from>): Likewise.
(<hetzner-image-protection>): Likewise.
(%hetzner-default-server-image): Change simple variable to a memoized
procedure.
(hetzner-api-server-create): Adjust user accordingly.
(hetzner-api-images): New procedure.

Change-Id: I9544708c878971a2c776c80b9a4ee06078d5ce61

This fixes a regression introduced in commit a2ef2bcbfd7 ("machine: hetzner:
Allow connections using ssh-agent"), where having no ssh-key would cause the
early Hetzner provisioning to fail due to the lack of SSH authentication.

* gnu/machine/hetzner.scm (%hetzner-ssh-key-file): New parameter.
(<hetzner-configuration>) [ssh-public-key]: Compute default according to the
value of the private ssh-key field.  Introduce an indirection via...
(hetzner-configuration-ssh-public-key): ... this new procedure, to honor
%hetzner-ssh-key-file.
(hetzner-configuration-ssh-key): Likewise for the private ssh-key.
(hetzner-configuration-ssh-key-fingerprint): Rename to...
(public-key->fingerprint): ... this, taking just the public key as argument.
Update doc.
(hetzner-configuration-ssh-key-public): Rename to...
(public-key->string-with-type): ...this, for clarity, and accept just a
public-key object.  Update doc.
(hetzner-machine-ssh-key): Exit early with #f when no ssh key is provided.
(temporary-ssh-key-file): New procedure.
(hetzner-machine-ssh-key-create): Assert a public key is defined.  Adjust
calls to renamed procedures, and adjust for the `hetzner-api-server-create'
API change.
(hetzner-machine-enable-rescue-system): Refine doc and fix code path when
ssh-key is #f.
(hetzner-machine-rescue-install-os): Document.
(hetzner-machine-provision): Refine doc. Remove extraneous sleep and #:unwind
argument. Limit ssh-session dynamic scope to where it's needed.
(cleanup-temporary-ssh-key/maybe): New procedure.
(deploy-hetzner): Create and use a temporary SSH key when none is defined, and
clean it up when done or on errors.
* gnu/machine/hetzner/http.scm (hetzner-api-server-create): Make ssh-keys a
keyword argument, and fix execution when it's #f.
(hetzner-api-server-enable-rescue-system): Likewise.
* tests/machine/hetzner.scm ("deploy-machine-mock-with-unprovisioned-server"):
Adjust test.
* tests/machine/hetzner/http.scm (create-server)
("hetzner-api-server-create-unit")
("hetzner-api-server-enable-rescue-system-unit")
("hetzner-api-actions-integration")
("hetzner-api-server-enable-rescue-system-integration"): Likewise.
* doc/guix.texi (Invoking guix deploy): Precise what happens when 'ssh-key' is
 #f in hetzner-configuration, and suggest declaratively authorizing your SSH
key.

Change-Id: I812b348fb553f3b5aebd0bf66850c6ecb9e06653

* gnu/machine/hetzner.scm (hetzner-configuration): Add ipv4 and ipv6
fields. Export accessors.
* gnu/machine/hetzner/http.scm (hetnzer-api-primary-ips): New function.
(<hetzner-primary-ip>): New json mapping.
(hetzner-api-server-create): Pass IP addresses in request.
* doc/guix.texi (Invoking guix deploy): Document it.

Change-Id: I44509cc98e041762dc483e876566e79bde85b26a
Signed-off-by: Ludovic Courtès <ludo@gnu.org>

Change-Id: I316652aff7418af4b8e83bea24638b1513f8aa97

* Makefile.am (SCM_TESTS): Add test modules.
* doc/guix.texi: Add documentation.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add modules.
* gnu/machine/hetzner.scm: Add hetzner-environment-type.
* gnu/machine/hetzner/http.scm: Add HTTP API.
* po/guix/POTFILES.in: Add Hetzner modules.
* tests/machine/hetzner.scm: Add machine tests.
* tests/machine/hetzner/http.scm Add HTTP API tests.

Change-Id: I276ed5afed676bbccc6c852c56ee4db57ce3c1ea
Signed-off-by: Ludovic Courtès <ludo@gnu.org>