Some perf-probe commands do symbol_init() but doesn't do exit call.

This fixes that to call symbol_exit() and releases machine if needed.

This also merges init_vmlinux() and init_user_exec() because both of
them are doing similar things.  (init_user_exec() just skips init
vmlinux related symbol maps)

Changes from v2:
 - Not to set symbol_conf.try_vmlinux_path in init_symbol_maps()
   (Thanks to Namhyung Kim!)
Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: "David A. Long" <dave.long@linaro.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: yrl.pp-manager.tt@hitachi.com
Link: http://lkml.kernel.org/r/20140206053204.29635.28334.stgit@kbuild-fedora.yrl.intra.hitachi.co.jpSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>