Fix INSERT options for PostgreSQL for INSERT+SELECT

Fix INSERT options for PostgreSQL for INSERT+SELECT

Fix handling of $insertOptions in
DatabasePostgres::insertSelect

Looks like this change:

https://gerrit.wikimedia.org/r/#/c/3962/
(or 646a9490f74f3841803299a4e4d2d5677c5f1bba)

mishandled badly INSERT IGNORE (instead of
silently broken support for it it introduced
PHP error).

Looks like we have no unit test to cover
the use of Database::insertSelect in the code.

Change-Id: I4f7d8c9bd9e413d8ffa23c1d0c0628a25c28d45c