build/init: support Red Hat and CentOS for kexec
edeploy: Don't start rsync if no add_only

As reported by users, if the add_only is missing the rsync is clearly
not doing something nice since it will break many files.

This commit add a check to insure that an existing and non-empty file
exists unless it will cancel the update process.
server/upload.py: fix setting vars in the configure script.
detect.py: Adding net device businfo

While trying to keep a constant interface naming, it is useful to have
the bus path which represent the PCI path to the device.

This PCI path is supposed to be fixed across the same HW product and so
could be used to detect a physical port on a system.

A typical output will be:
    ('network', 'eth0', 'businfo', 'pci@0000:00:19.0'),

Note that on VMs this parameter will not be populated.