Cleanup vinyl engine initialization

Vinyl engine initialization is done in two steps: first we create the
engine class and then we call ->init() method, which creates vinyl
environment. There's no reason not to create the environment right in
the engine class constructor, so let's move it there and drop ->init().
Also, let's pass engine parameters to the engine constructor, just like
we do in case of memtx, instead of reading the config from the engine
implementation.