Add 'GetRunningBindingDirPath' function

Add 'GetRunningBindingDirPath' function

Add 'GetRunningBindingDirPath' function that returns the binding
directory path (the path to the directory that contains the binding).

FYI:
- 'Binding directory path' is the path to the directory that contains
a binding binding launched by the binder.
- 'Binder root directory path' is the path specified at binder launch
using '--rootdir' option. If no option is specified, binder root
directory is set to the current directory.

SPEC-AGL: SPEC-3009

Change-Id: I34b3d17710ebc2bf06541a00ca7f8d7189f6aa18
Signed-off-by: Jonathan Aillet <jonathan.aillet@iot.bzh>