Fix module ELF/debuginfo file path search.

I assume what happened here is that when we added the debuginfo root
prefix business, and expanded the search for vmlinux, that we never did
that for modules; but not sure.  Anyway, this fixes the module search so
it is similar to searching for vmlinux.
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Status Job ID Name Coverage
  Test
passed build-ubuntu16 #1402

00:04:22

passed pages #1403

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