import: Fix ordering of subdomain availability check.
import: Fix ordering of subdomain availability check.

When you're importing with --destroy-rebuild-database, we need to
check subdomain availability after we've cleared out the database;
otherwise, trying to reuse the same subdomain doesn't work.

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