coredump: save process container parent cmdline

coredump: save process container parent cmdline

Process container parent is the process used to start processes with a new
user namespace - e.g systemd-nspawn, runc, lxc, etc.

There is not standard way how to find such a process - or I do not know
about it - hence I have decided to find the first process in the parent
process hierarchy with a different mount namespace and different
/proc/self/root's inode.

I have decided for this criteria because in ABRT we take special care
only if the crashed process runs different code than installed on the
host. Other processes with namespaces different than PID 1's namespaces
are just processes running code shipped by the OS vendor and bug
reporting tools can get information about the provider of the code
without the need to deal with changed root and so on.