linuxNodeInfoCPUPopulate: avoid used-uninitialized via a test

linuxNodeInfoCPUPopulate: avoid used-uninitialized via a test

* tests/nodeinfotest.c (linuxTestCompareFiles): Don't use
nodeinfo->member uninitialized.  linuxNodeInfoCPUPopulate requires
that some of its nodeinfo members (including threads) be initialized
upon input.  The nodeinfotest.c program lacked the initialization,
while the only other use (nodeGetInfo) did perform it.
It's not trivial to move the initialization into the function,
since nodeGetInfo sets at least one member after clearing the
buffer but before calling linuxNodeInfoCPUPopulate.