upgrade: Add "must be run as root" check.
upgrade: Add "must be run as root" check.

The logic and text is based on scripts/lib/upgrade-zulip.

andersk/zulip,dhcrzf/zulip,synicalsyntax/zulip,timabbott/zulip,shubhamdhama/zulip,jackrzhang/zulip,timabbott/zulip,kou/zulip,Galexrt/zulip,andersk/zulip,timabbott/zulip,showell/zulip,jackrzhang/zulip,shubhamdhama/zulip,zulip/zulip,rishig/zulip,brockwhittaker/zulip,showell/zulip,showell/zulip,timabbott/zulip,timabbott/zulip,eeshangarg/zulip,shubhamdhama/zulip,synicalsyntax/zulip,brainwane/zulip,brainwane/zulip,timabbott/zulip,brainwane/zulip,rht/zulip,brockwhittaker/zulip,jackrzhang/zulip,punchagan/zulip,rht/zulip,dhcrzf/zulip,tommyip/zulip,mahim97/zulip,jackrzhang/zulip,synicalsyntax/zulip,eeshangarg/zulip,showell/zulip,kou/zulip,punchagan/zulip,brainwane/zulip,shubhamdhama/zulip,mahim97/zulip,rht/zulip,eeshangarg/zulip,zulip/zulip,dhcrzf/zulip,synicalsyntax/zulip,rishig/zulip,synicalsyntax/zulip,kou/zulip,zulip/zulip,punchagan/zulip,showell/zulip,tommyip/zulip,hackerkid/zulip,tommyip/zulip,Galexrt/zulip,punchagan/zulip,brockwhittaker/zulip,brainwane/zulip,punchagan/zulip,rishig/zulip,andersk/zulip,Galexrt/zulip,tommyip/zulip,kou/zulip,synicalsyntax/zulip,mahim97/zulip,andersk/zulip,hackerkid/zulip,hackerkid/zulip,zulip/zulip,shubhamdhama/zulip,mahim97/zulip,zulip/zulip,rishig/zulip,rht/zulip,eeshangarg/zulip,showell/zulip,eeshangarg/zulip,rishig/zulip,jackrzhang/zulip,brockwhittaker/zulip,andersk/zulip,andersk/zulip,kou/zulip,hackerkid/zulip,rht/zulip,brainwane/zulip,andersk/zulip,shubhamdhama/zulip,jackrzhang/zulip,timabbott/zulip,kou/zulip,Galexrt/zulip,kou/zulip,zulip/zulip,jackrzhang/zulip,rishig/zulip,brockwhittaker/zulip,punchagan/zulip,mahim97/zulip,brockwhittaker/zulip,rishig/zulip,tommyip/zulip,dhcrzf/zulip,dhcrzf/zulip,eeshangarg/zulip,punchagan/zulip,hackerkid/zulip,brainwane/zulip,Galexrt/zulip,mahim97/zulip,dhcrzf/zulip,synicalsyntax/zulip,showell/zulip,zulip/zulip,dhcrzf/zulip,eeshangarg/zulip,tommyip/zulip,Galexrt/zulip,hackerkid/zulip,Galexrt/zulip,rht/zulip,shubhamdhama/zulip,hackerkid/zulip,tommyip/zulip,rht/zulip