Added an FSTN describing the good day scenario of a tape drive's status within

the vdqmd daemon with the drive comming up, having a tape mounted, and then
having the tape unmounted.

castor/tape/doc/fstns/vdqmDriveStatesAndTapeserverd.dot

+digraph fstn {
+  rankdir=TD;
+  size="8,5"
+  center=1
+  node [shape = rectangle];
+  "INIT"             -> "UP"               [ label = "received\nVDQM_UNIT_UP\nfrom tapeserverd"];
+  "UP"               -> "STARTING"         [ label = "allocated drive\nto a tapegatewayd request"];
+  "STARTING"         -> "SUBMITTED"        [ label = "send\nVDQM_CLIENTINFO\nto tapeserverd"];
+  "SUBMITTED"        -> "ASSIGNED"         [ label = "received\nVDQM_UNIT_ASSIGN\nfrom tapeserverd"];
+  "ASSIGNED"         -> "MOUNTED"          [ label = "received\nVDQM_VOL_MOUNT\nfrom tapeserverd"];
+  "MOUNTED"          -> "WAIT_FOR_UNMOUNT" [ label = "received\nVDQM_UNIT_RELEASE\nfrom tapeserverd\nand no new request"];
+  "MOUNTED"          -> "STARTING"         [ label = "received\nVDQM_UNIT_RELEASE\nfrom tapeserverd\nand new request"];
+  "WAIT_FOR_UNMOUNT" -> "UP"               [ label = "received\nVDQM_VOL_UNMOUNT\nfrom tapeserverd"];
+}