block/ssh: Bump minimum libssh version to 0.8.7

block/ssh: Bump minimum libssh version to 0.8.7

It has been over two years since RHEL-8 was released, and thus per the
platform build policy, we no longer need to support RHEL-7 as a build
target. So from the RHEL-7 perspective, we do not have to support
libssh v0.7 anymore now.

Let's look at the versions from other distributions and operating
systems - according to repology.org, current shipping versions are:

             RHEL-8: 0.9.4
      Debian Buster: 0.8.7
 openSUSE Leap 15.2: 0.8.7
   Ubuntu LTS 18.04: 0.8.0 *
   Ubuntu LTS 20.04: 0.9.3
            FreeBSD: 0.9.5
          Fedora 33: 0.9.5
          Fedora 34: 0.9.5
            OpenBSD: 0.9.5
     macOS HomeBrew: 0.9.5
         HaikuPorts: 0.9.5

* The version of libssh in Ubuntu 18.04 claims to be 0.8.0 from the
name of the package, but in reality it is a 0.7 patched up as a
Frankenstein monster with patches from the 0.8 development branch.
This gave us some headaches in the past already and so it never worked
with QEMU. All attempts to get it supported have failed in the past,
patches for QEMU have never been merged and a request to Ubuntu to
fix it in their 18.04 distro has been ignored:

 https://bugs.launchpad.net/ubuntu/+source/libssh/+bug/1847514

Thus we really should ignore the libssh in Ubuntu 18.04 in QEMU, too.

Fix it by bumping the minimum libssh version to something that is
greater than 0.8.0 now. Debian Buster and openSUSE Leap have the
oldest version and so 0.8.7 is the new minimum.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Tested-by: Richard W.M. Jones <rjones@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Acked-by: Richard W.M. Jones <rjones@redhat.com>
Message-Id: <20210519155859.344569-1-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>