perf buildid-cache: Use lsdir() for looking up buildid caches

perf buildid-cache: Use lsdir() for looking up buildid caches

Use new lsdir() for looking up buildid caches. This changes logic a bit
to ignore all dot files, since the build-id cache must not start with
dot.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Hemant Kumar <hemant@linux.vnet.ibm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20160511135217.23943.94596.stgit@devbox
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>