Add support for upgrade script to be called during cartridge upgrades.

Trello: https://trello.com/c/JdLrIBk2/173-2-upgrade-process-improvement (origin_runtime_173)
Bug 984811

As is the case with a very old cartridge, if both
OPENSHIFT_POSTGRES_VERSION and OPENSHIFT_POSTGRESQL_VERSION do
not exist in postgresql/env directory, create one with '8.4'.

Hard coding this value should be OK, since 8.4 was the only supported
version of PostgreSQL for the cartridge this condition ever applies.
Merge pull request #3091 from pmorie/dev/upgrades

Merged by openshift-bot
Merge pull request #3092 from BanzaiMan/dev/hasari/bz984811

Merged by openshift-bot