Make sure to create directories for log and pid files before starting.
Make :merge_config_file! public, it's public for SidekiqInstance, too.

SidekiqInstance has its :merge_config_file! and :sane? methods defined
public, while SidekiqConfiguration has them defined private. Inside
SidekiqConfiguration::get(), these methods are called via send(). This
prevents them from being called within the configuration code in the
client. However, for SidekiqInstance, making them private and calling
them from SidekiqConfiguration via send() feels odd. Plus, these methods
do not really need to be protected from the client anyway, so let's
just make them public.