Fix pot internal state in start-cleanup

[grembo]

This introduces a distinct state called "doa" (dead on arrival), which is also an allowed prerequisite
for going to state stopping.

[grembo]

Tested locally:

# grep ip= /opt/pot/jails/cloneme/conf/pot.conf
ip=lo0|garbage
# pot start cloneme
###>  No ipv4 address found for cloneme
error: Invalid value for '--host <host>': invalid IP address syntax
###>  cloneme failed to start
# cat /tmp/pot_status_cloneme
pot.status=stopped

[grembo]

And of course:

# grep ip= /opt/pot/jails/cloneme/conf/pot.conf
ip=lo0|127.0.0.1
# pot start cloneme
===>  Starting the pot cloneme
ip6addrctl: socket(UDP): Protocol not supported
# cat /tmp/pot_status_cloneme 
pot.status=started

[grembo]

@pizzamig 0.15.2 maybe?

[pizzamig]

A different approach could be to remove the status file, in case of failure.
But it can add additional complexity and corner cases