tools: Add replacement for missing dbus_validate_path() on D-Bus 1.4

The replacement is based on code from D-Bus 1.6.
android: Fix const to non-const issue on android-tester

According to definition from hardware/bluetooth.h, the "val" field does
not have const modifier.

Fix clang errors like:

android/android-tester.c:760:14: error: initializing 'void *' with an
expression of type 'const char (*)[18]' discards qualifiers
[-Werror,-Wincompatible-pointer-types-discards-qualifiers]