Merge pull request open-horizon#2532 from bmpotter/make-agbot-url-opt…

…ional

Issue SDO-support 110: make HZN_AGBOT_URL optional in agent-install.sh

tested rpm installation in docker container

horizon 2.10.0

horizon 2.9.1

horizon 2.9.0

horizon 2.8.0

horizon 2.7.0

horizon 2.6.0

horizon 2.5.0

Merge pull request open-horizon#297 from michaeldye/refactor/exchange…

…_config_from_envvar

move exchange URL to envvar from config file