code cleanup in serverLazyInit

code cleanup in serverLazyInit

Summary:
Just some small cleanup...

(1) rename to `ServerLazyInit.saved_state_init` and `.full_init`

(2) Shifted the logic about reporting "Could not load saved state" out of `full_init` into its only caller, `saved_state_init`

(3) Remove unused parameters

(4) Moved the "Lazy_lev=Init, load_state_approach=None" logic out of serverLazyInit.saved_state_init, and into its caller ServerInit.

The end goal of this cleanup is to have functions with clear single purposes and names that reflect that, and to move the important strategic decisions about what to do about saved-state higher up the callstack.

Reviewed By: arxanas

Differential Revision: D13539901

fbshipit-source-id: 3aec58939675e0d5be3f2eb74726778f1b623332