control: mapped_floor: Support floor offset param

Add support to the mapped floor action to read the name of an optional
floor offset parameter from the JSON.  If it's there, then any time a
floor is calculated it will add that offset to the floor value before
setting it.  This is added at the level of the key value, so that
particular offset is only applied to floors found in that section.

For example, if
     "key": 27,
     "floor_offset_parameter": "floor_altitude_offset",
     ...

is in the JSON config, it will add whatever value is in the
floor_altitude_offset parameter to the floor value it calculates when
that key value is valid.

This allows one to do something like set an floor offset based on the
current altitude.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I39ab6287a6948058981aed1cdbae5e91aade80d9
2 files changed