Strip backslashes from the output of rabbitmqctl

The output of `rabbitmqctl(1)` escapes backslashes. This was documented
in the `rabbitmqctl` man page[1] but was removed when the manpage was
converted to DocBook XML[2].

This change causes extraneous backslashes to be stripped to prevent
this module from misreading escaped characters in regular expressions
and repeatedly applying the same change.

[1]:
https://github.com/rabbitmq/rabbitmq-server/blob/16418a9488e15c4d8ef3bfa9fce69190fb8ec796/docs/rabbitmqctl.1.pod#output-escaping
[2]:
rabbitmq/rabbitmq-server@60c14ba#diff-b96d4e7ccd3d984656b8ab3534e6b460

lib/puppet/provider/rabbitmq_user_permissions/rabbitmqctl.rb

@@ -16,6 +16,7 @@ def self.users(name, vhost)
     unless @users[name]
       @users[name] = {}
       rabbitmqctl('-q', 'list_user_permissions', name).split(/\n/).each do |line|
+        line = self::strip_backslashes(line)
         if line =~ /^(\S+)\s+(\S*)\s+(\S*)\s+(\S*)$/
           @users[name][$1] =
             {:configure => $2, :read => $4, :write => $3}
@@ -102,4 +103,9 @@ def set_permissions
     end
   end
 
+  def self.strip_backslashes(string)
+    # See: https://github.com/rabbitmq/rabbitmq-server/blob/16418a9488e15c4d8ef3bfa9fce69190fb8ec796/docs/rabbitmqctl.1.pod#output-escaping
+    string.gsub(/\\\\/, '\\')
+  end
+
 end