Update to use new sectionless config.get() from Hydra-base config-in-db changes

The current `config.get()` function imported from `hydra_base` returns values from a section-based .ini file while the more recent config-in-db version does not use sections.

Existing calls to `config.get()` in Hydra-client need updating to match this new format.

See https://github.com/hydraplatform/hydra-base/issues/157