acceptance: use stable URLs for the Debian and Ubuntu installer

The kernel and initrd hashes seem to have changed for the Bionic
aarch64 installer, causing BootLinuxConsole.test_aarch64_xlnx_versal_virt
to fail.  Correct the paths to use the previous binaries instead of
the latest.  Do the same for the Lenny alpha installer for
consistency, even though those are unlikely to change.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200810092941.154911-1-pbonzini@redhat.com>

tests/acceptance/boot_linux_console.py

@@ -337,7 +337,7 @@ def test_aarch64_xlnx_versal_virt(self):
         """
         images_url = ('http://ports.ubuntu.com/ubuntu-ports/dists/'
                       'bionic-updates/main/installer-arm64/'
-                      'current/images/')
+                      '20101020ubuntu543.15/images/')
         kernel_url = images_url + 'netboot/ubuntu-installer/arm64/linux'
         kernel_hash = '5bfc54cf7ed8157d93f6e5b0241e727b6dc22c50'
         kernel_path = self.fetch_asset(kernel_url, asset_hash=kernel_hash)
@@ -821,7 +821,7 @@ def test_alpha_clipper(self):
         :avocado: tags=machine:clipper
         """
         kernel_url = ('http://archive.debian.org/debian/dists/lenny/main/'
-                      'installer-alpha/current/images/cdrom/vmlinuz')
+                      'installer-alpha/20090123lenny10/images/cdrom/vmlinuz')
         kernel_hash = '3a943149335529e2ed3e74d0d787b85fb5671ba3'
         kernel_path = self.fetch_asset(kernel_url, asset_hash=kernel_hash)