CA-400789 Do not exclude parentless VDIs from cacheing

Though a VDI might be parentless when it is first attached, a snapshot
might be taken at any time and that should be allowed cacheing for the
read-only parts of the chain at once, instead of being forced to wait
until the guest is restarted.

Signed-off-by: Tim Smith <tim.smith@cloud.com>

drivers/blktap2.py

@@ -1010,10 +1010,6 @@ def get_o_direct_capability(self, options):
         elif not ((self.target.vdi.sr.handles("nfs") or self.target.vdi.sr.handles("ext") or self.target.vdi.sr.handles("smb"))):
             self.__o_direct = True
             self.__o_direct_reason = "SR_NOT_SUPPORTED"
-        elif not (options.get("rdonly") or self.target.vdi.parent):
-            util.SMlog(self.target.vdi)
-            self.__o_direct = True
-            self.__o_direct_reason = "NO_RO_IMAGE"
         elif options.get("rdonly") and not self.target.vdi.parent:
             self.__o_direct = True
             self.__o_direct_reason = "RO_WITH_NO_PARENT"