Add missing eCryptfs translation to FsNames

It was causing the error message to be

    'overlay' is not supported over <unknown>

instead of

    'overlay' is not supported over ecryptfs

Signed-off-by: Iago López Galeiras <iago@kinvolk.io>

daemon/graphdriver/driver_linux.go

@@ -67,6 +67,7 @@ var (
 		FsMagicAufs:        "aufs",
 		FsMagicBtrfs:       "btrfs",
 		FsMagicCramfs:      "cramfs",
+		FsMagicEcryptfs:    "ecryptfs",
 		FsMagicExtfs:       "extfs",
 		FsMagicF2fs:        "f2fs",
 		FsMagicGPFS:        "gpfs",