Fix LifecycleEnvironment.{build,create}

> When a new lifecycle environment is created, it must either:
>
> * Reference some other lifecycle environment via the "prior" field.
> * Have a name of "Library". Note that within a given organization, there
>   can only be a single lifecycle environment with a name of "Library".

Override method `LifecycleEnvironment.build`, thus allowing one to easily create
new lifecycle environments. Incidentally, this also prevents a recursive death
spiral from occurring when `build` or `create` are called.

Update `tests/foreman/api/test_multiple_paths.py` to take advantage of this
change.