More granular logging when proc file not exist

KernelCpuProcReader records a horrifying exception when the proc file
does not exist, creating confusion that this is the source of error.
Bug: 74074575
Test: KernelCpuProcReaderTest

Change-Id: Ib35e114cd78e1e9f424adf66da5eb85da9f6fe5f
1 file changed