Prevent destroy-environment when desired.
Fixed error construction and format. Renamed vars for clarity and conformity.
Cleaned up error-related code based on review.
Made code readable
Environment variable manipulation is behind cmds for block/unblock operation.
Code readability improvement.
Mock command for tests.
More verbose command purpose for help.
Fixing up error messages and mock.
Using DeepEquals for map comparison.
Merge pull request #1107 from anastasiamac/flag-prevent-destroy-environment

Prevent destroy-environment when desired.

Customers and stakeholders want to be able to prevent accidental damage to their Juju deployments by activating environment settings which prevent destroy-environment. 

When on, this setting needs to be manually deactivated prior to the protected operations being allowed.

"force destroy-environment" ignores this setting.