iotests/051: Add test for empty filename

Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NFam Zheng <famz@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

tests/qemu-iotests/051

@@ -232,6 +232,7 @@ echo === Leaving out required options ===
 echo
 
 run_qemu -drive driver=file
+run_qemu -drive driver=file,filename=
 run_qemu -drive driver=nbd
 run_qemu -drive driver=raw
 run_qemu -drive file.driver=file

tests/qemu-iotests/051.out

@@ -221,6 +221,9 @@ QEMU X.Y.Z monitor - type 'help' for more information
 Testing: -drive driver=file
 QEMU_PROG: -drive driver=file: The 'file' block driver requires a file name
 
+Testing: -drive driver=file,filename=
+QEMU_PROG: -drive driver=file,filename=: The 'file' block driver requires a file name
+
 Testing: -drive driver=nbd
 QEMU_PROG: -drive driver=nbd: NBD server address missing
 

tests/qemu-iotests/051.pc.out

@@ -319,6 +319,9 @@ QEMU X.Y.Z monitor - type 'help' for more information
 Testing: -drive driver=file
 QEMU_PROG: -drive driver=file: The 'file' block driver requires a file name
 
+Testing: -drive driver=file,filename=
+QEMU_PROG: -drive driver=file,filename=: The 'file' block driver requires a file name
+
 Testing: -drive driver=nbd
 QEMU_PROG: -drive driver=nbd: NBD server address missing