lscpu: don't abort if cache size is unknown

There are systems where the size file does not exist. Most badly even
lscpu -p would abort allthough it does not use the size:
$ lscpu -p
lscpu: error: cannot open
/sys/devices/system/cpu/cpu0/cache/index0/size: No such file or directory

This patch does not abort in this case and prints "unknown size" in
human-readable case. For examle on this qemu pcc test machine:
$ lscpu
Architecture:          ppc
CPU op-mode(s):        32-bit
Byte Order:            Big Endian
CPU(s):                1
On-line CPU(s) list:   0
Thread(s) per core:    1
Core(s) per socket:    1
Socket(s):             1
Model:                 Power Macintosh
BogoMIPS:              33.25
L1d cache:             unknown size
L1i cache:             unknown size

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
lscpu: cleanup, use _PATH_SYS_CPU/NODE

This make most lines shorter than 80 chars again (tab-witdh 4).

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
tests: add lscpu dump for ppc cpu with no cache size

Taken from qemu-system-ppc (qemu 1.7) machine with installed
debian 7.4 wheezy, kernel 3.2.0-4-powerpc.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
tests: cleanup, remove unused lscpu output

All these files are not used since a292bbde or 0d86c70a.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
Merge branch 'fix-lscpu-cache' into travis

* fix-lscpu-cache:
  tests: cleanup, remove unused lscpu output
  tests: add lscpu dump for ppc cpu with no cache size
  lscpu: cleanup, use _PATH_SYS_CPU/NODE
  lscpu: don't abort if cache size is unknown
travis-ci: cat /etc/apt/sources.list