Make Debian guest detection more reliable

/etc/issue is far from being a reliable source for OS detection as it
can be changed by a user without affecting any OS functionality. As
newer Debian systems run systemd by default, check for /etc/os-release
and fallback to lsb_release for older Debian versions. Check hashicorp#7625 for
a similar issue. Even lsb_release is not manatory, therefore keep the
current code of parsing /etc/issue to avoid regressions.

plugins/guests/debian/guest.rb

@@ -4,7 +4,17 @@ module VagrantPlugins
   module GuestDebian
     class Guest < Vagrant.plugin("2", :guest)
       def detect?(machine)
-        machine.communicate.test("cat /etc/issue | grep 'Debian'")
+        machine.communicate.test <<-EOH.gsub(/^ {10}/, "")
+          if test -r /etc/os-release; then
+            source /etc/os-release && test xdebian = x$ID
+          elif test -x /usr/bin/lsb_release; then
+            /usr/bin/lsb_release -i 2>/dev/null | grep -q Debian
+          elif test -r /etc/issue; then
+            cat /etc/issue | grep 'Debian'
+          else
+            exit 1
+          fi
+        EOH
       end
     end
   end