Explicitly use 3.10 kernel

The linux-yocto-dev branch was rebased to 3.12, and this
required a new kern-tools git, which we didn't have.

See https://lists.yoctoproject.org/pipermail/poky/2013-October/009368.html

Fix this by explicitly using 3.10 kernel with the updated
kern-tools from oe-core master.

https://bugzilla.gnome.org/show_bug.cgi?id=710684