add_example tool directory pathing not as expected in docker

[satchelbaldwin]

find_specification_write_location in adhoc.py always returns None for the location when using add_example from within the docker container.

https://github.com/jataware/beaker-kernel/blob/1e8ea3e54ecb48ad77b4f2126e80079b2fbbf0e7/beaker_kernel/lib/integrations/adhoc.py#L284

data.basedirs is ['/usr/local/share/beaker/data/biome'] at the time of the issue.

INTEGRATIONS_DIR env var works as a temporary fix for single user cases for now.