Stop modifying names for internal computations

Currently the name used internally is modified and holds the shortened
name of the nodes/instances. This has caused issues before, since we
always have to strip the suffix from input data and reapply it if we
need to send data back to Ganeti.

This patch changes the code such that the names are never modified, only
the alias, and all the internal computations can forget about the common
suffix addition/removal.