test_mattermost_importer: Fix buggy use of wrong paths.
test_mattermost_importer: Fix buggy use of wrong paths.

This worked for me when testing locally because it was using a
constant path, and so was accessing the product under `var/` of the
previous test run.

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