fine-grained hwentry config override

fine-grained hwentry config override

== Before:
adding

device {
 vendor EMC
 product FOO
 checker tur
}

resets all hwentry vars not specified in the block to internal
defaults ... losing the precious bits in the internal default
hwtable.

== After:
adding the same block retains all info present in the
default hwtable and override only the bits specified in the conf
file.