perf tools: Support running perf binaries with a dash in their name

Previously the part behind "perf-" was interpreted as an internal perf
command. If the suffix could not be handled, the execution was stopped.
This makes it impossible to launch perf binaries that got renamed to
have the `perf-` prefix. This is e.g. the case for appimages (e.g.
"perf-x86_64.AppImage"), but would also apply to all other scenarios
where users symlink or rename perf themselves:

Status quo with the broken behavior:

  $ ln -s ./perf ./perf-custom-suffix
  $ ./perf-custom-suffix list
  cannot handle custom-suffix internally$

Also note the missing newline at the end of the error message.

With this patch applied, the above works properly:

  $ ./perf-custom-suffix list

  List of pre-defined events (to be used in -e):
  ...

Signed-off-by: Milian Wolff <milian.wolff@kdab.com>
Acked-by: David Ahern <dsahern@gmail.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Yao Jin <yao.jin@linux.intel.com>
Link: http://lkml.kernel.org/r/20170911111422.31903-1-milian.wolff@kdab.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>