Use the exist? method in Vagrantfile to avoid undifined method exists?

Change-Id: I0181d6fd17ecae835c2ec2dbf1971b6eda87bdaf
Signed-off-by: Cosmin Cojocar <[email protected]>

Author: ccojocar

hack/ci/Vagrantfile-debian

@@ -16,7 +16,7 @@ Vagrant.configure("2") do |config|
     v.cpus = cpus
   end
 
-  if File.exists?("./ssh-config")
+  if File.exist?("./ssh-config")
     config.ssh.config = "./ssh-config"
   end
 

hack/ci/Vagrantfile-fedora

@@ -17,7 +17,7 @@ Vagrant.configure("2") do |config|
     v.cpus = cpus
   end
 
-  if File.exists?("./ssh-config")
+  if File.exist?("./ssh-config")
     config.ssh.config = "./ssh-config"
   end
 

hack/ci/Vagrantfile-flatcar

@@ -25,7 +25,7 @@ Vagrant.configure("2") do |config|
     v.cpus = cpus
   end
 
-  if File.exists?("./ssh-config")
+  if File.exist?("./ssh-config")
     config.ssh.config = "./ssh-config"
   end
   config.ssh.connect_timeout = 30

hack/ci/Vagrantfile-ubuntu

@@ -16,7 +16,7 @@ Vagrant.configure("2") do |config|
     v.cpus = cpus
   end
 
-  if File.exists?("./ssh-config")
+  if File.exist?("./ssh-config")
     config.ssh.config = "./ssh-config"
   end