If cursor blinking is disabled no screen updates will happen and
fbcon_fbt subtests will fail, so lets enable cursor blink while
running this test and restore to the previous value when exiting it.

v4:
- renaming restore fd (Dhinakaran)
- saving previous value as char (Dhinakaran)
- skipping test if not able to open cursor blink file (Dhinakaran)

Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>