perf trace record: handle commands correctly

Because the perf-trace shell scripts hard-coded the use of the
perf-record system-wide param, a perf trace record session was always
system wide, even if it was given a command.

If given a command, perf trace record now only records the events for
the command, as users expect.

If no command is given, or if the '-a' option is used, the recorded
events are system-wide, as before.

root@tropicana:~# perf trace record syscall-counts ls -al
root@tropicana:~# perf trace
              ls-23152 [000] 39984.890387: sys_enter: NR 12 (0, 0, 0, 0, 0, 0)
              ls-23152 [000] 39984.890404: sys_enter: NR 9 (0, 0, 0, 0, 0, 0)

root@tropicana:~# perf trace record syscall-counts -a ls -al
root@tropicana:~# perf trace
    npviewer.bin-22297 [000] 39831.102709: sys_enter: NR 168 (0, 0, 0, 0, 0, 0)
              ls-23111 [000] 39831.107679: sys_enter: NR 59 (0, 0, 0, 0, 0, 0)

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Acked-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>