Fix the gbs export doesn't generate patches when packaging non-native package.

Fix the gbs export doesn't generate patches when packaging non-native package.

Reason:
The packages can be divided into 2 categories: native packages and non-native (or upstream) packages.
Please refer to https://docs.tizen.org/platform/reference/gbs/gbs-maintenance-models/.
If the package has export branch and upstream branch, but the export branch is not based on upstream,
gbs will export this package as no-native without auto-generate patches.

Solution:
Export the package as native package if the export branch is not based on upstream.

Change-Id: I16f12acc9ab2111f8f5b2e966bbf6b4d56ae5086
Signed-off-by: wanchao-xu <wanchao.xu@samsung.com>