check: add ability to exclude a test or group

check: add ability to exclude a test or group

Add the ability to exclude a test or whole test group from a test
run. Thus a user can explicitly decide which tests to skip like in
this example where one wants all of the 'block' group but block/001.

block/002 (remove a device while running blktrace)
    0.835s           ...
    runtime  + test  ...
[  363.132053] run blktests block/002 at 2017-05-19 13:01:56
[  363.136844] scsi host0: scsi_debug: version 1.86 [20160430]
[  363.136844]   dev_size_mb=8, opts=0x0, submit_queues=1, statistics=0
[  363.138819] scsi 0:0:0:0: Direct-Access     Linux    scsi_debug       0186 PQ: 0 ANSI: 7
[  363.199172] sd 0:0:0:0: [sda] 16384 512-byte logical blocks: (8.39 MB/8.00 MiB)
[  363.207053] sd 0:0:0:0: [sda] Write Protect is off
block/002 (remove a device while running blktrace)           [passed]

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
[Omar: use associative array, make explicit run take precedence over -x]
Signed-off-by: Omar Sandoval <osandov@fb.com>