Prevent running from a different Kayobe configuration repository

There are various ways in which it is possible to operate Kayobe
incorrectly. One example is executing Kayobe from a different Kayobe
configuration repository than the one referred to by the
KAYOBE_CONFIG_PATH environment variable.

While this shouldn't necessarily cause any errors, it may lead to
unexpected results if the operator assumes they are operating against
the configuration in the current directory.

This change adds a validation step that checks for this case and fails
the command early if found.

Change-Id: I709884bbd7edebf1d409f39c11f293560e987506