Close leaked file descriptors
Close leaked file descriptors

Explicit call to 'close()' is required on file descriptors allocated
from 'epoll::create()', which is missing for the 'EpollContext' and
'VringWorker'. This patch enforces to close the file descriptors by
reusing the Drop trait of the 'File' struct.

Signed-off-by: Bo Chen <e07d1ca6585eb2004364a325debafd9e0629e530@intel.com>

rust-vmm/vhost