broker: Set date header in mails
broker: Set date header in mails

RFC5322 requires a 'Date' header to be set. If it is not provided, mail
clients might display strange send dates.

Change-Id: I84c03008657992174bf2bce84b9ac7b5de37a94f
Bug-Url: https://bugzilla.redhat.com/1229774
Signed-off-by: Roman Mohr <6da0130c5aeef94e5bbaabadbf8017270be25c64@redhat.com>

oVirt/ovirt-hosted-engine-ha,oVirt/ovirt-hosted-engine-ha,oVirt/ovirt-hosted-engine-ha,oVirt/ovirt-hosted-engine-ha