test_signup: Update deactivate realm tests for subdomains.
test_signup: Update deactivate realm tests for subdomains.

We add a new test to make sure we cover the potential race condition
with the realm being deactivated after starting the registration
process.

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