fix for host template management

#ensure? will now go to server and compare list of templates there with what is provided in configuration 
#create will update that list with zabbixapi.templates#mass_add as it looks to be the only way to do that, #create_or_update does not recognize this particular change. 

I've also made loop in #create a bit more "ruby-esque" and fixed the case when "templates" is a string.