Added spec test to check msg is truncated to 1.megabyte

mylog.log

@@ -0,0 +1 @@
+# Logfile created on 2017-11-21 19:15:42 +0000 by logger.rb/56438

spec/util/vmdb-logger_spec.rb

@@ -96,8 +96,14 @@
   end
 
   context "long messages" do
+    before(:each) do
+      @logger = VMDBLogger.new(@log)
+    end
+
     it "truncates long messages when max_message_size is set" do
-      # TODO Add test body!
+      msg = "a" * 1_572_864 # 1.5 mb in bytes
+      _, message = @logger.formatter.call(:error, Time.now.utc, "", msg).split("-- : ")
+      expect(message.strip.size).to eq((1.megabyte))
     end
   end