chore: determine correct env var
chore: determine correct env var

[#180904926](https://www.pivotaltracker.com/story/show/180904926)

Signed-off-by: James Norman <b453bec9a77bf7b89572c103be1bc62eefe72d6e@vmware.com>

pivotal-cf/brokerapi,pivotal-cf/brokerapi