Update client.shared.mail

In the hopes of unifying 3 different wrappers to the
standard email library, that do slightly different
things, update the already existing client.shared.mail
library to include:

* An API to send emails
* A class that takes care of sending emails, based
  on settings defined in global_config.ini.

This aims to replace:

* client.shared.base_utils.send_email
* scheduler.email_manager

The API was re-designed, and support of HTML email was
added.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
Change server.frontend to use the new mail API

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
Remove client.shared.base_utils.send_email API

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
scheduler: Replace email_manager module with mail

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
scheduler.scheduler_models: Change failed/aborted job notification

In order to not spam the job report mailing lists, when
a job failed or aborted, send an email to the autotest
grid admin with the status instead. This way, the grid
admin can take action and eventually fix the problems.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
global_config.ini: Remove unused settings

Now that all reporting code is using the new sections,
EMAIL and NOTIFICATION, we can get rid of the keys
in the other sections.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>