providers/virtualbox: retry list vms [GH-2831]

CHANGELOG.md

@@ -10,6 +10,8 @@ BUG FIXES:
   - core: Asking for input works even in consoles that don't support
     hiding input. [GH-3119]
   - core: Adding a box by path in Cygwin on Windos works. [GH-3132]
+  - providers/virtualbox: Make more internal interactions with VBoxManage 
+    retryable to avoid spurious VirtualBox errors. [GH-2831]
   - provisioners/ansible: Request SSH info within the provision method,
     when we know its available. [GH-3111]
 

plugins/providers/virtualbox/driver/version_4_3.rb

@@ -72,7 +72,7 @@ module VagrantPlugins
             networks << $1.to_s if line =~ /^Name:\s+(.+?)$/
           end
 
-          execute("list", "vms").split("\n").each do |line|
+          execute("list", "vms", retryable: true).split("\n").each do |line|
             if line =~ /^".+?"\s+\{(.+?)\}$/
               info = execute("showvminfo", $1.to_s, "--machinereadable", :retryable => true)
               info.split("\n").each do |inner_line|
@@ -222,7 +222,7 @@ module VagrantPlugins
             end
           end
 
-          output = execute("list", "vms")
+          output = execute("list", "vms", retryable: true)
           match = /^"#{Regexp.escape(specified_name)}" \{(.+?)\}$/.match(output)
           return match[1].to_s if match
           nil