Spawn daemon and args not used if disposable

[vasco-santos]

After discussing this issue on ipfs/interop#60#issuecomment-483207296, if we spawn a disposable daemon it will not start automatically.

In this context, as we need to start it manually, the possible args that we can provide on spawn options are not used in start. I think that we should merge the args that we provide via options in spawn with eventual args that can be provided through start (https://github.com/ipfs/js-ipfsd-ctl#ipfsdstartflags-callback).

What do you think @hugomrdias ?

[hugomrdias]

need to merge this #308 first