Implement get-value on the wire protocol

Note that testing has currently been done using strings, so there may
still be issues with minimum lengths, etc. However, testing set + get
over the wire using strings works as intended.

Now we'll need to implement smack control within the get/set methods
using the existing smack helpers in the library.

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>