Greetings Jothi -
Not sure if you're still having issues with this, but if you're doing a standard build/package where the war is being put into the <project_home>/target folder, I'd suggest removing the optional <warFile> element and allowing the tomcat-plugin to use the default settings. This seems to work quite well for me, using a mvn clean tomcat:redeploy will build and push up the new war. Which reminds me, using the 'clean' goal prior to any build is a good practice to get into, as it assures that you're getting the freshest bits.
My current configuration is:
Keep in mind that by default the tomcat-plugin will expect your manager login to be "admin' "<blank>", in other words the user is 'admin' and there is no password set....these are configured in the <tomcat_home>/conf/tomcat-users.xml file.
Hope this helps someone!