devtool: second fix for running from a different directory

devtool: second fix for running from a different directory

Do not change change current working directory permanently, but, only
for the duration of tinfoil initialization instead. The previous fix
caused very unintuitive behavior where using relative paths were solved
with respect to the builddir instead of the current working directory.
E.g. calling "devtool extract zlib ./zlib" would always create create
srctree in ${TOPDIR}/zlib, independent of the users cwd.

(From OE-Core rev: 4c7f159b0e17a0475a4a4e9dc4dd012e3d2e6a1f)

Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>