perf script: Allow the generated script to be a path

perf script: Allow the generated script to be a path

Allow the script generated by "perf script -g <language>" to be a file
path and the language determined by the file extension.

This is useful in testing so that the generated script file can be
written to a test directory.

Committer testing:

  $ perf record ls a.a
  ls: cannot access 'a.a': No such file or directory
  [ perf record: Woken up 2 times to write data ]
  [ perf record: Captured and wrote 0.003 MB perf.data (7 samples) ]
  $ perf script -g python
  generated Python script: perf-script.py
  $ perf script -g myscript.py
  generated Python script: myscript.py
  $ diff -u perf-script.py myscript.py
  $ tail myscript.py
  def trace_unhandled(event_name, context, event_fields_dict, perf_sample_dict):
  		print(get_dict_as_string(event_fields_dict))
  		print('Sample: {'+get_dict_as_string(perf_sample_dict['sample'], ', ')+'}')

  def print_header(event_name, cpu, secs, nsecs, pid, comm):
  	print("%-20s %5u %05u.%09u %8u %-20s " % \
  	(event_name, cpu, secs, nsecs, pid, comm), end="")

  def get_dict_as_string(a_dict, delimiter=' '):
  	return delimiter.join(['%s=%s'%(k,str(v))for k,v in sorted(a_dict.items())])
  $

Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Leo Yan <leo.yan@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sandipan Das <sandipan.das@amd.com>
Cc: Yujie Liu <yujie.liu@intel.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>