fix default values not taken in build_command()
use a more specific message for mandatory parameter errors.
stop the comandline building as soon as an error is raised

whatever the results of a step check_mandatory, check_controls, ...
all steps until build command line was executed.
now we stop as soon an error is raised
ignore files geretated by coverage
mob2execd is in weird state if pidfile cannot be created

if pidfile already exists the process was stuck endlessly
when we open the daemnon context so the process is daemonized but
the mater is not start

if the directory of pidfile is not writable we observe the same behavior

now if the file exists or the directory is not wraitable
the daemon will not start
add all parameters in the evaluator.
adapt the build_actor execution to the new job status/error mechanisms.
Merge branch 'feature_command_builder' of https://github.com/mobyle2/mobyle2.exec_engine into feature_command_builder