perf kvm: Use strtol for walking guestmount directory

Only want to process directories under the guestmnount directory that
have a pid as a name (ie, all digits). Other entries in the guestmount
directory should be ignored.  There is already a check that requires the
first character of each entry to be a digit, but atoi is used to convert
the directory name to a pid. For example if guestmount contains a
directory with the name 1foo, atoi converts it to a pid of 1 and a
machine is created with a pid of 1. This is wrong; this directory really
should be ignored. Use strtol to do that.

Signed-off-by: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1343616875-6455-1-git-send-email-dsahern@gmail.com


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