Add decorator that requires a lock for Drac management driver

Add decorator that requires a exclusive lock for set_boot_device
in Drac management driver. Default lock is shared, which
is useful for non-interfering operation, like get_boot_device.
Have exclusive lock with an action, can avoid multiple threads 
to modify the node at same time. This is necessary for 
changing the boot device for a node.

Change-Id: I8482da70cbb859a8da05025f2ee12a1e614f7928
Merge "Add decorator that requires a lock for Drac management driver"