CA-186161: Don't mmap raw VDIs, just read/write
CA-186161: Don't mmap raw VDIs, just read/write

When the file descriptor is closed, the memory maps remain until a major heap
GC. For the case of these raw VDIs they cannot then be unplugged from dom0
because the tapdisk cannot shutdown because the device is still in use.

Signed-off-by: Si Beaumont <a0992b7f1f450b4c7716d34b81a2d6f0877ae11a@citrix.com>

euanh/xen-api,thomassa/xen-api,rafalmiel/xen-api,jjd27/xen-api,simonjbeaumont/xen-api,rafalmiel/xen-api,thomassa/xen-api,euanh/xen-api,jjd27/xen-api,simonjbeaumont/xen-api,Frezzle/xen-api,thomassa/xen-api,simonjbeaumont/xen-api,euanh/xen-api,rafalmiel/xen-api,jjd27/xen-api,thomassa/xen-api,euanh/xen-api,simonjbeaumont/xen-api,Frezzle/xen-api,srowe/xen-api,rafalmiel/xen-api,thomassa/xen-api,rafalmiel/xen-api,srowe/xen-api,jjd27/xen-api,Frezzle/xen-api,simonjbeaumont/xen-api,jjd27/xen-api,rafalmiel/xen-api,Frezzle/xen-api,euanh/xen-api,euanh/xen-api,Frezzle/xen-api,jjd27/xen-api,thomassa/xen-api,srowe/xen-api,srowe/xen-api,simonjbeaumont/xen-api,srowe/xen-api