One of the upsert related tests is unstable (sometimes even hanging
until isolationtester's step timeout is reached). Based on preliminary
analysis that might be a problem outside of just that test, but not
really related to EPQ and triggers.  Disable for now, to get the
buildfarm greener again.

Discussion: https://postgr.es/m/20191004222437.45qmglpto43pd3jb@alap3.anarazel.de
Backpatch: 9.6-, just like c8841199.