MessageDictTest: Fix nondeterministic query counts.
MessageDictTest: Fix nondeterministic query counts.

This fixes an issue with a nondeterministic number of database queries
being used in fetching bulk messages from the database.  The source of
the problem was that we were fetching _all_ messages, not just the 600
that had been created by the test, and thus if the set of streams
present in messages in the test fixtures (which is random) changes,
the number of streams used (and thus number of queries) would change.

brainwane/zulip,tommyip/zulip,ryanbackman/zulip,rht/zulip,amanharitsh123/zulip,verma-varsha/zulip,showell/zulip,eeshangarg/zulip,dhcrzf/zulip,dhcrzf/zulip,rishig/zulip,verma-varsha/zulip,ryanbackman/zulip,Galexrt/zulip,eeshangarg/zulip,kou/zulip,showell/zulip,jackrzhang/zulip,vaidap/zulip,verma-varsha/zulip,brockwhittaker/zulip,SmartPeople/zulip,jackrzhang/zulip,Galexrt/zulip,jphilipsen05/zulip,shubhamdhama/zulip,jrowan/zulip,j831/zulip,eeshangarg/zulip,tommyip/zulip,christi3k/zulip,jrowan/zulip,tommyip/zulip,synicalsyntax/zulip,mahim97/zulip,hackerkid/zulip,punchagan/zulip,brainwane/zulip,eeshangarg/zulip,mahim97/zulip,jphilipsen05/zulip,timabbott/zulip,ryanbackman/zulip,timabbott/zulip,synicalsyntax/zulip,j831/zulip,andersk/zulip,dhcrzf/zulip,vabs22/zulip,SmartPeople/zulip,andersk/zulip,hackerkid/zulip,tommyip/zulip,kou/zulip,punchagan/zulip,tommyip/zulip,brockwhittaker/zulip,timabbott/zulip,Galexrt/zulip,vaidap/zulip,amanharitsh123/zulip,synicalsyntax/zulip,christi3k/zulip,zulip/zulip,kou/zulip,zulip/zulip,rishig/zulip,eeshangarg/zulip,showell/zulip,jrowan/zulip,synicalsyntax/zulip,hackerkid/zulip,verma-varsha/zulip,rht/zulip,kou/zulip,rht/zulip,brainwane/zulip,jackrzhang/zulip,dhcrzf/zulip,amanharitsh123/zulip,jackrzhang/zulip,showell/zulip,amanharitsh123/zulip,vabs22/zulip,brainwane/zulip,christi3k/zulip,eeshangarg/zulip,zulip/zulip,punchagan/zulip,kou/zulip,vabs22/zulip,dhcrzf/zulip,Galexrt/zulip,Galexrt/zulip,showell/zulip,kou/zulip,mahim97/zulip,jackrzhang/zulip,SmartPeople/zulip,Galexrt/zulip,hackerkid/zulip,shubhamdhama/zulip,mahim97/zulip,shubhamdhama/zulip,andersk/zulip,timabbott/zulip,rishig/zulip,andersk/zulip,vaidap/zulip,SmartPeople/zulip,zulip/zulip,rishig/zulip,christi3k/zulip,shubhamdhama/zulip,amanharitsh123/zulip,zulip/zulip,jrowan/zulip,andersk/zulip,jphilipsen05/zulip,mahim97/zulip,timabbott/zulip,dhcrzf/zulip,vabs22/zulip,j831/zulip,tommyip/zulip,jackrzhang/zulip,brockwhittaker/zulip,christi3k/zulip,mahim97/zulip,amanharitsh123/zulip,andersk/zulip,ryanbackman/zulip,rht/zulip,timabbott/zulip,hackerkid/zulip,punchagan/zulip,vaidap/zulip,SmartPeople/zulip,rht/zulip,shubhamdhama/zulip,brainwane/zulip,brockwhittaker/zulip,jrowan/zulip,brainwane/zulip,tommyip/zulip,brockwhittaker/zulip,verma-varsha/zulip,vabs22/zulip,punchagan/zulip,verma-varsha/zulip,Galexrt/zulip,j831/zulip,rishig/zulip,synicalsyntax/zulip,rht/zulip,kou/zulip,ryanbackman/zulip,synicalsyntax/zulip,zulip/zulip,andersk/zulip,jphilipsen05/zulip,dhcrzf/zulip,synicalsyntax/zulip,vaidap/zulip,rishig/zulip,rht/zulip,shubhamdhama/zulip,zulip/zulip,shubhamdhama/zulip,eeshangarg/zulip,timabbott/zulip,hackerkid/zulip,j831/zulip,brockwhittaker/zulip,jackrzhang/zulip,christi3k/zulip,rishig/zulip,vabs22/zulip,jphilipsen05/zulip,j831/zulip,vaidap/zulip,jphilipsen05/zulip,hackerkid/zulip,SmartPeople/zulip,punchagan/zulip,brainwane/zulip,punchagan/zulip,showell/zulip,ryanbackman/zulip,showell/zulip,jrowan/zulip