linuxNodeGetCPUStats: Correctly handle cpu prefix

linuxNodeGetCPUStats: Correctly handle cpu prefix

To retrieve node cpu statistics on Linux system, the
linuxNodeGetCPUstats function simply uses STRPREFIX() to match the cpuid
with the one read from /proc/stat. However, as the file is read line by
line it may happen, that some CPUs share the same prefix. So if user
requested stats for the first CPU, which is offline, then there's no
cpu1 in the stats file so the one that we match is cpu10. Which is
obviously wrong. Fortunately, the IDs are terminated by a space, so we
can utilize that.

Signed-off-by: Bing Bu Cao <mars@linux.vnet.ibm.com>