Fix bundle serialisation exception type
Fix bundle serialisation exception type

The original exception only exists in this one line,
so is undefined, causing the except to raise instead.
Change to the exception which the simplejson.loads()
function actually generates on load error.

Change-Id: Ib9e01e20c28de6ddc176578572bc3f4f730e5d78

Linaro/lava-server,Linaro/lava-server,Linaro/lava-server,Linaro/lava-server