The cmd/storagenode/main.go is a big mess right now with so many
unneeded config structures initialized and shared by several
subcommands.
There are many instances where the config structure of one subcommand
is mistakenly used for another subcommand.
This changes is an attempt to clean up the main.go by moving the
subcommands to a separate `cmd_*.go` files with separate config structures
for each subcommand.
Resolves https://github.com/storj/storj/issues/5756
Change-Id: I85adf2439acba271c023c269739f7fa3c6d49f9d
periodically create and delete a temp file in the storage directory
to verify writability. If this check fails, shut the node down.
Change-Id: I433e3a8d1d775fc779ae78e7cf3144a05ffd0574
