Workaround a problem in couchdb.

In some cases (compactation, db reset) the update to a document which
has previously existed can be silently ignored. This makes feat fail
at to start up.

The bug in couchdb is:
https://issues.apache.org/jira/browse/COUCHDB-1415
Add a service command to delete all the descriptors from the database
regardless of their type.

This is usefull for the reset script.
Add more debug before killing the agent when his descriptor gets modified.
Add debugging.
Imporce logging and error handling of host agent spawning agents.
Increase timeout for starting agent to 20 seconds.

The motivation here is the behaviour of frf. Comparing the logs of the
master and the slave agencies I can see that it takes 7 seconds there
between master calling "feat -X ..." and the slave logging the first line
to the log. There is simply not enough time for the slave to start up.
Make sure task is not cancelled twice.

It could happen during the forced termination procedure.
Merge branch 'release-0.29.x'