Add FSTYPE__configured() (where FSTYPE is one of sysfs, procfs, debugfs,
tracefs) interface that returns bool state of the filesystem mount:

  true - mounted, false - not mounted

It will not try to mount the filesystem.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Raphael Beamonte <raphael.beamonte@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/1441180605-24737-13-git-send-email-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>