Prepare only drives requested by test

Signed-off-by: Jan Musial <jan.musial@intel.com>

Author: Jan Musial

test/functional/tests/conftest.py

@@ -256,7 +256,7 @@ def base_prepare(item):
 
         RamDisk.remove_all()
 
-        for disk in TestRun.dut.disks:
+        for disk in TestRun.disks.values():
             disk_serial = get_disk_serial_number(disk.path)
             if disk.serial_number != disk_serial:
                 raise Exception(