Description of problem:Do not send "sync errata" email when there are no sync errata updates after repository synchronization.The mail for  syncing an errata should only be sent when actual errata updates are available or they are greater than zero. If a daily sync is applied then a mail is sent even if there are no errata updates avilable. 


Version-Release number of selected component (if applicable):
Satellite 6

How reproducible:
Always

Steps to Reproduce:
1.users = User.where(:mail => 'abc')  #<-- Create account add valid email and change email here
User.current = users.first
repo = Katello::Repository.find(383)   #<--- id of "Red Hat Enterprise Linux 7 Server RPMs x86_64 7Server"
last_updated = repo.repository_errata.order('updated_at ASC').last.try(:updated_at)
if last_updated
 errata = Katello::Erratum.where(:id => repo.repository_errata.where('katello_repository_errata.updated_at > ?', last_updated.to_datetime).pluck(:erratum_id))
 puts errata.size
 MailNotification[:sync_errata].deliver(:users => users, :repo => repo, :errata => errata)
end
~~

If there is a daily sync schedule then its annoying to receive daily mail with 0 errata 


Actual results:
A mail is received stating for errata update with 0 errata 

Expected results:
A mail for errata updates should only be triggered if the errata count is more than zero.

Additional info: