devtool: refactor exec_fakeroot

devtool: refactor exec_fakeroot

Provide a function exec_fakeroot_no_d which does the same like
exec_fakeroot does, but is usable independenlty from bitbake. This
allows to use the fanction from scripts where the d variable is not
available.

Signed-off-by: Adrian Freihofer <adrian.freihofer@siemens.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>