Fix testOooUnoMimemapper

Due to a5157949 cloudooo will retry 10 times before raising thus take this into account
Raise rather than swallow.

Test do pass at
https://nexedi.erp5.net/test_result_module/20191227-20A35E0F

/reviewed-on !21
1 job for master in 0 seconds
Status Job ID Name Coverage
  External
failed Cloudooo.UnitTest-Master

00:23:03