perf symbols: Add path to Ubuntu kernel debuginfo file

Ubuntu places the kernel debuginfo in /usr/lib/debug/boot/vmlinux-*

Signed-off-by: Anton Blanchard <anton@samba.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
echo Link: http://lkml.kernel.org/n/tip-`ranpwd -l 24`@git.kernel.org
Link: http://lkml.kernel.org/r/20140909091152.2698c0f7@kryten
[ Adapted it to use the perf.data file kernel version as in 0a7e6d1b

 ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>