perf tools: Fix legacy events symbol separator parsing

perf tools: Fix legacy events symbol separator parsing

Fixing legacy symbol events parsing. We can't support single slash
separator, like 'cycles/u', because it conflicts with non empty terms,
like 'cycles/period/u'.

Keeping only '//' and ':' separator for these events:
  cycles//u
  cycles:k

And removing '/' separator support, which is not working
anymore. Also adding automated tests for above events.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20190213123246.4015-5-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>