Refactor the options handling in defaults.py to allow the --jobs
option have varing specific parameters. The option supports 'none',
'max' and 'half' or a fraction to divide the number of CPUs or
an integer value which is the number of jobs. The --no-smp has
been removed.
The host specific modules have been changed to set the number of
CPUs in the defaults table.
Fixed the --keep-going to clean up is --always-clean is provided
even if the build has an error.
