qemu-iotests: fix filename containing checks

Commit cce293a2 moved some functions from common.config to
common.rc, but the error messages still reference the old file
location.
Signed-off-by: NCleber Rosa <crosa@redhat.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20181004161852.11673-5-crosa@redhat.com>
Signed-off-by: NLaurent Vivier <laurent@vivier.eu>

tests/qemu-iotests/common.rc

@@ -170,7 +170,7 @@ if [ ! -e "$TEST_DIR" ]; then
 fi
 
 if [ ! -d "$TEST_DIR" ]; then
-    echo "common.config: Error: \$TEST_DIR ($TEST_DIR) is not a directory"
+    echo "common.rc: Error: \$TEST_DIR ($TEST_DIR) is not a directory"
     exit 1
 fi
 
@@ -179,7 +179,7 @@ if [ -z "$REMOTE_TEST_DIR" ]; then
 fi
 
 if [ ! -d "$SAMPLE_IMG_DIR" ]; then
-    echo "common.config: Error: \$SAMPLE_IMG_DIR ($SAMPLE_IMG_DIR) is not a directory"
+    echo "common.rc: Error: \$SAMPLE_IMG_DIR ($SAMPLE_IMG_DIR) is not a directory"
     exit 1
 fi