perf sched latency: prettify printed table

Before:

 ---------------------------------------------------------------------------------------------------------------
  Task                  |   Runtime ms  | Switches | Average delay ms | Maximum delay ms | Maximum delay at     |
 ---------------------------------------------------------------------------------------------------------------
  ...                   |               |          |                  |                  |
  git:24540             |    336.622 ms |       10 | avg:    0.032 ms | max:    0.062 ms | max at: 115610.111046 s
  git:24541             |      0.457 ms |        1 | avg:    0.000 ms | max:    0.000 ms | max at:  0.000000 s
 -----------------------------------------------------------------------------------------
  TOTAL:                |    396.542 ms |      353 |
 ---------------------------------------------------

After:

 -----------------------------------------------------------------------------------------------------------------
  Task                  |   Runtime ms  | Switches | Average delay ms | Maximum delay ms | Maximum delay at       |
 -----------------------------------------------------------------------------------------------------------------
  ...                   |               |          |                  |                  |
  git:24540             |    336.622 ms |       10 | avg:    0.032 ms | max:    0.062 ms | max at: 115610.111046 s
  git:24541             |      0.457 ms |        1 | avg:    0.000 ms | max:    0.000 ms | max at:      0.000000 s
 -----------------------------------------------------------------------------------------------------------------
  TOTAL:                |    396.542 ms |      353 |
 ---------------------------------------------------

Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>