volttron_home not starting without full path.

[riley206]

Description
when setting VOLTTRON_HOME to a relative path using export VOLTTRON_HOME=, It will (most of the time) throw an error not allowing you to start the platform.

To Reproduce
Steps to reproduce the behavior:

1. Install volttron
2. export VOLTTRON_HOME=/some/relative/path
3. start the platform
4. See error volttron.server.main(210) DEBUG: opts.instancename None

Expected behavior
I expect volttron to understand this relative path and correctly use it.

Operating System:

• OS: Ubuntu (WSL)
• volttron-core [develop]