sar: Allow user to select block devices to display

sar: Allow user to select block devices to display

Add new option "--dev=<dev_list>" to allow the user to specify which
block devices to display. This option is to be used with option -d.
Sample output:

$ sar -dp
Linux 4.4.14-200.fc22.x86_64 (home) 05/12/18 _x86_64_ (8 CPU)

10:35:29          DEV       tps     rkB/s     wkB/s   areq-sz [...]
10:35:31          sda     17.00    142.00     14.00      9.18
10:35:31         sda1      0.00      0.00      0.00      0.00
10:35:31         sda2      0.00      0.00      0.00      0.00
10:35:31         sda3      0.00      0.00      0.00      0.00
10:35:31         sda4      0.00      0.00      0.00      0.00
10:35:31         sda5      0.00      0.00      0.00      0.00
10:35:31         sda6      0.00      0.00      0.00      0.00
10:35:31         sda7      0.00      0.00      0.00      0.00
10:35:31         sda8     15.50    142.00      4.00      9.42
10:35:31         sda9      0.00      0.00      0.00      0.00
10:35:31        sda10      0.00      0.00      0.00      0.00
10:35:31        sda11      1.50      0.00     10.00      6.67
[...]

$ sar -dp --dev=sda,sda8
Linux 4.4.14-200.fc22.x86_64 (home) 05/12/18 _x86_64_ (8 CPU)

10:35:29          DEV       tps     rkB/s     wkB/s   areq-sz [...]
10:35:31          sda     17.00    142.00     14.00      9.18
10:35:31         sda8     15.50    142.00      4.00      9.42
[...]

Signed-off-by: Sebastien GODARD <sysstat@users.noreply.github.com>