oeqa/utils/gitarchive: Handle case where parent is only on origin

oeqa/utils/gitarchive: Handle case where parent is only on origin

The parent code currently assumed that any parent branch is locally
checked out which may not be the case.

Use the local branch by default but fall back to the origin. This
also means removing the later saftey check as the branch may not exist
locally.

This fixes the autobuilder resulttool test pushing code.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>