tools lib traceevent: Fix memory leak in pretty_print()

tools lib traceevent: Fix memory leak in pretty_print()

Commit 12e55569a244 "tools lib traceevent: Use helper trace-seq in print
functions like kernel does" added a extra trace_seq helper to process
string arguments like the kernel does it. But the difference between the
kernel and the userspace library is that the kernel's trace_seq structure
has a static allocated buffer. The userspace one has a dynamically
allocated one. It requires a trace_seq_destroy(), otherwise it produces
a nasty memory leak.

Cc: stable@vger.kernel.org # 3.14+
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20140422192330.6bb09bf8@gandalf.local.home
Signed-off-by: Jiri Olsa <jolsa@redhat.com>