`st2 pack install` should not depend on `packs` pack

Background

Currently, st2 ships some default packs:

• core
• chatops
• default
• linux
• packs

These are placed in /opt/stackstorm/packs directory, which is the default system pack directory (referred here) that all other packs installed later via st2 pack install command will also be placed.

In docker-ized environment, usually this directory will be mounted as a volume, so that users do not lose their packs contents between container restart. But it is also possible and common way that they bind-mount host directory to /opt/stackstorm/packs instead of using docker volume, which will cause users end up with the empty directory and cannot access those system default packs easily. Now, without packs pack content there, they cannot use st2 pack install at all.

Suggested solution

• Make st2 pack install independent from packs pack
• Put all packs shipped with st2 onto StackStorm-Exchange and make them installable via st2 pack install command

Start by tracing the st2 pack install command and how it depends on the packs pack in the default /opt/stackstorm/packs directory. Compare that behavior with Docker bind-mount usage and the proposed StackStorm-Exchange installation flow; done means installation works without the packs pack and shipped packs can be installed from the Exchange.