The `stacks` sub-command sometimes misses stacks

[Steve Kemp]

When a stack is present in multiple states it might get excluded.

• Imagine you create a stack, then delete it.
• Later you create a stack with the same name.

This results in two stacks in the list-stack output :

• One in DELETE_COMPLETE state
• One in CREATE_COMPLETE state

Depending on the random ordering this might get excluded. We need to build/maintain a list of the stack-stats not a simple key=>value hash, which will overwrite the stack-details.