populate_db: Fix cache flushing when rebuilding test database.
populate_db: Fix cache flushing when rebuilding test database.

This fixes a similar problem to the last commit; we don't use
memcached with the test database, so we don't need to flush memcached
when rebuilding it.

(And if we try, we'll get exceptions trying to access the relevant
settings).

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