Lean on docker's db more heavily; do some basic paranoid checking.

(In my defense, the first draft of this codebase came from a hackathon!)
Rename GET /containers/:id API handler from 'inspect' to 'get'.

Export 'inspect' for usage in other places and make _paranoid_inspect private.
Remove unused subs; pull in 'inspect' instead of duplicating.
Remove tables from db that duplicate what docker already tracks.
Better error handling for determining true_pid.
Move the hex-string regex into Agent::Util.
Add is_active to container_condition

This'll be needed when different sets of container
conditions will be stored, but not active (such as
with different test sets).