queue: Suppress error mail from brief rabbitmq downtimes.
queue: Suppress error mail from brief rabbitmq downtimes.

Details in comment.  Together with a few previous commits, this should
completely eliminate sending error mail to admins when the RabbitMQ
server is simply restarted and comes back up normally.

shubhamdhama/zulip,timabbott/zulip,tommyip/zulip,rht/zulip,timabbott/zulip,andersk/zulip,kou/zulip,shubhamdhama/zulip,tommyip/zulip,brainwane/zulip,showell/zulip,brainwane/zulip,brainwane/zulip,eeshangarg/zulip,rht/zulip,dhcrzf/zulip,zulip/zulip,hackerkid/zulip,rht/zulip,kou/zulip,tommyip/zulip,punchagan/zulip,rishig/zulip,shubhamdhama/zulip,brainwane/zulip,tommyip/zulip,rht/zulip,tommyip/zulip,kou/zulip,rishig/zulip,rht/zulip,shubhamdhama/zulip,kou/zulip,rishig/zulip,timabbott/zulip,kou/zulip,jackrzhang/zulip,punchagan/zulip,dhcrzf/zulip,rht/zulip,eeshangarg/zulip,synicalsyntax/zulip,hackerkid/zulip,eeshangarg/zulip,jackrzhang/zulip,brainwane/zulip,synicalsyntax/zulip,dhcrzf/zulip,kou/zulip,rishig/zulip,rht/zulip,andersk/zulip,tommyip/zulip,andersk/zulip,zulip/zulip,zulip/zulip,andersk/zulip,jackrzhang/zulip,brainwane/zulip,hackerkid/zulip,jackrzhang/zulip,dhcrzf/zulip,synicalsyntax/zulip,hackerkid/zulip,timabbott/zulip,timabbott/zulip,jackrzhang/zulip,showell/zulip,punchagan/zulip,jackrzhang/zulip,hackerkid/zulip,kou/zulip,andersk/zulip,hackerkid/zulip,punchagan/zulip,showell/zulip,eeshangarg/zulip,synicalsyntax/zulip,eeshangarg/zulip,shubhamdhama/zulip,brainwane/zulip,shubhamdhama/zulip,andersk/zulip,shubhamdhama/zulip,synicalsyntax/zulip,synicalsyntax/zulip,dhcrzf/zulip,showell/zulip,timabbott/zulip,timabbott/zulip,dhcrzf/zulip,zulip/zulip,zulip/zulip,rishig/zulip,tommyip/zulip,rishig/zulip,dhcrzf/zulip,andersk/zulip,punchagan/zulip,showell/zulip,punchagan/zulip,eeshangarg/zulip,eeshangarg/zulip,jackrzhang/zulip,synicalsyntax/zulip,zulip/zulip,showell/zulip,hackerkid/zulip,punchagan/zulip,rishig/zulip,zulip/zulip,showell/zulip