ERP5TypeFunctionalTestCase: take screenshot and dump the page on error

This is not really for errors during the test itself, but for errors when
ERP5TypeFunctionalTestCase manipulates browser to execute selenium test.
10 jobs for feat/seleniumserver in 0 seconds
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-TestRunner2

01:41:07

failed ERP5.UnitTest-JEROME.own-distributor

06:09:32

failed ERP5.UnitTest-TestRunner2

07:20:22

passed ERP5.CodingStyleTest-TestRunner2

00:40:06

passed ERP5.CodingStyleTest-TestRunner2

05:36:48

canceled ERP5.UnitTest-JEROME.own-distributor

00:53:12

failed ERP5.UnitTest-JEROME.own-distributor

05:54:11

canceled ERP5.UnitTest-JEROME.own-distributor

00:10:08

failed ERP5.UnitTest-JEROME.own-distributor

failed ERP5.UnitTest-TestRunner2

03:50:29