Update test-helpers

Signed-off-by: Tim Jarratt <tjarratt@pivotallabs.com>
Remove use of ENV vars

Signed-off-by: Tammer Saleh <tammer@pivotallabs.com>
Use AsUser from cf-test-helpers instead of CreateHomeConfig()

Signed-off-by: Tammer Saleh <tammer@pivotallabs.com>
Bump test helpers