Sensor list time improvements

A lot inefficient code was added since these commands
were originally implemented. Fix the caches and add yield
method calls where calls were expensive.

Tested: ipmitool sensor list for 104 sensors was 18 seconds
over lan

Change-Id: I9ec2d42303839257629001f4cbb5cc1417989754
Signed-off-by: James Feist <james.feist@linux.intel.com>
4 files changed