command/cooker/knotty: Fix memres handling of command environment changes

command/cooker/knotty: Fix memres handling of command environment changes

If the environment changes, we need memory resident bitbake to adapt to those
changes. This adds in functionality to handle this alongside the configuration
option handling code. This means that the common usage:

MACHINE=X bitbake Y

now works with the memory resident server.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>