StringIO#write accepts multiple args in ruby 2.5

As of this commit, which landed in ruby 2.5.0, both IO and StringIO
write now accept multiple arguments:
ruby/ruby@aeaeb4b

Somehow this was causing the automation engine spec, specifically, the
"writes to the logger synchronously" example to spin at 100% cpu,
perhaps because write was failing with argument errors.

Seen originally in:
ManageIQ/manageiq-automation_engine#296

lib/vmdb/loggers/io_logger.rb

@@ -7,10 +7,12 @@ def initialize(logger, level = :info, prefix = nil)
       super()
     end
 
-    def write(string)
-      @buffer ||= ""
-      @buffer << string
-      dump_buffer if string.include?("\n")
+    def write(*args)
+      args.each do |arg|
+        @buffer ||= ""
+        @buffer << arg
+        dump_buffer if arg.include?("\n")
+      end
     end
 
     def <<(string)