Handle multiple paths in the SECONDARY_STORAGE variable.

  Some devices list multiple paths for the SECONDARY_STORAGE
  variable, I.E. /storage/sdcard1:/storage/usbdisk
  When attempting to browse the device using the BT Ftp protocol
  accessing EXTERNAL STORAGE would result in failed path
  being mapped, and cause the system to fall into a loop.

  Its also assumed that the device will have only one real
  SECONDARY_STORAGE with the rest being linked in some
  manner back to the first.

Change-Id: I3edf73f2b7e31cbaa84cc9c5f22a49c9ffb12347