email_to is an array not string; method .each is needed

revert part of commit 0d136c216cacc9e0b7c2147cba11e828d52bd41d
https://bugzilla.redhat.com/show_bug.cgi?id=1101819
migrate miq_alerts options: store email_to addresses in an array

https://bugzilla.redhat.com/show_bug.cgi?id=1093588