Use constants for well-known exit statuses

Use a constant instead of 4 or 1.
Put less code in main package, more in spmarun

It is easier to unit test without root privileges if logic is contained
in the application package rather than the main package.
CAF::Process splits on your behalf

CAF::Process does the split on your behalf. Just
CAF::Process->new([$cmd]) will do.  Also, pass log => $self as a
parameter to get more traces.
Verify format of packager before attempting to use it

Verify packager before using it to prevent arbitrary Perl commands from
being executed by the eval if misformed.
image_create() now takes parameter (for image dir)

Make it easier to unit test the image_create() method by passing
SPMA_IMAGEDIR as a parameter.
Use pushargs() and rename imagedir_new to newdir