guests: rename LinuxShellExpandFailed error to ShellExpandFailed

Make the error generic for all guests (`DarwinShellExpandFailed` didn't
even exist) and not tied to synced folder.

lib/vagrant/errors.rb

@@ -304,10 +304,6 @@ module Vagrant
       error_key(:linux_nfs_mount_failed)
     end
 
-    class LinuxShellExpandFailed < VagrantError
-      error_key(:linux_shell_expand_failed)
-    end
-
     class LocalDataDirectoryNotAccessible < VagrantError
       error_key(:local_data_dir_not_accessible)
     end
@@ -444,6 +440,10 @@ module Vagrant
       error_key(:shared_folder_create_failed)
     end
 
+    class ShellExpandFailed < VagrantError
+      error_key(:shell_expand_failed)
+    end
+
     class SSHAuthenticationFailed < VagrantError
       error_key(:ssh_authentication_failed)
     end

plugins/guests/darwin/cap/shell_expand_guest_path.rb

@@ -14,7 +14,7 @@ module VagrantPlugins
           if !real_path
             # If no real guest path was detected, this is really strange
             # and we raise an exception because this is a bug.
-            raise DarwinShellExpandFailed
+            raise ShellExpandFailed
           end
 
           # Chomp the string so that any trailing newlines are killed

plugins/guests/linux/cap/shell_expand_guest_path.rb

@@ -17,7 +17,7 @@ module VagrantPlugins
           if !real_path
             # If no real guest path was detected, this is really strange
             # and we raise an exception because this is a bug.
-            raise LinuxShellExpandFailed
+            raise ShellExpandFailed
           end
 
           # Chomp the string so that any trailing newlines are killed

templates/locales/en.yml

@@ -463,11 +463,6 @@ en:
         that the NFS client software is properly installed, and consult any resources
         specific to the linux distro you're using for more information on how to
         do this.
-      linux_shell_expand_failed: |-
-        Vagrant failed to determine the shell expansion of the guest path
-        for one of your shared folders. This is an extremely rare error case
-        and most likely indicates an unusual configuration of the guest system.
-        Please report a bug with your Vagrantfile.
       machine_guest_not_ready: |-
         Guest-specific operations were attempted on a machine that is not
         ready for guest communication. This should not happen and a bug
@@ -591,6 +586,11 @@ en:
         %{path}
 
         Please create the folder manually or specify another path to share.
+      shell_expand_failed: |-
+        Vagrant failed to determine the shell expansion of a guest path
+        (probably for one of your shared folders). This is an extremely rare
+        error case and most likely indicates an unusual configuration of the
+        guest system. Please report a bug with your Vagrantfile and debug log.
       ssh_authentication_failed: |-
         SSH authentication failed! This is typically caused by the public/private
         keypair for the SSH user not being properly set on the guest VM. Please