tests: Move bot event code out of setUp().
tests: Move bot event code out of setUp().

This code is only used in one test, and having
the indirection of setUp partly obscured a
problem with the fact that our event message
is actually a wide dict that gets mutated
by `build_bot_request`.  We'll fix that soon,
but this is a pure code move for now.

shubhamdhama/zulip,zulip/zulip,showell/zulip,timabbott/zulip,rht/zulip,eeshangarg/zulip,hackerkid/zulip,shubhamdhama/zulip,brainwane/zulip,synicalsyntax/zulip,punchagan/zulip,kou/zulip,zulip/zulip,timabbott/zulip,synicalsyntax/zulip,hackerkid/zulip,rht/zulip,synicalsyntax/zulip,kou/zulip,kou/zulip,andersk/zulip,shubhamdhama/zulip,andersk/zulip,rht/zulip,rht/zulip,eeshangarg/zulip,kou/zulip,hackerkid/zulip,andersk/zulip,showell/zulip,eeshangarg/zulip,brainwane/zulip,rht/zulip,punchagan/zulip,eeshangarg/zulip,synicalsyntax/zulip,zulip/zulip,andersk/zulip,punchagan/zulip,eeshangarg/zulip,synicalsyntax/zulip,hackerkid/zulip,rht/zulip,zulip/zulip,zulip/zulip,punchagan/zulip,shubhamdhama/zulip,shubhamdhama/zulip,rht/zulip,shubhamdhama/zulip,zulip/zulip,showell/zulip,timabbott/zulip,showell/zulip,andersk/zulip,andersk/zulip,hackerkid/zulip,eeshangarg/zulip,timabbott/zulip,eeshangarg/zulip,timabbott/zulip,brainwane/zulip,timabbott/zulip,synicalsyntax/zulip,showell/zulip,timabbott/zulip,punchagan/zulip,punchagan/zulip,brainwane/zulip,shubhamdhama/zulip,brainwane/zulip,hackerkid/zulip,hackerkid/zulip,kou/zulip,brainwane/zulip,showell/zulip,zulip/zulip,punchagan/zulip,synicalsyntax/zulip,andersk/zulip,kou/zulip,kou/zulip,showell/zulip,brainwane/zulip