wic/utils/oe/misc.py: Preserve PATH when running native tools
Previously exec_native_cmd() would remove all items from PATH except for
the native sysroot. This can cause issues for the tools that are created
using create_wrapper().
Now instead of wiping out the PATH, run a sanity check to check if the
command is in the native sysroot.
Signed-off-by: Randy Witt <randy.e.witt@linux.intel.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
