m4: bhyve: Fix check for the required bhyve programs

bhyveload and bhyvectl wouldn't be checked otherwise as the configure
script wouldn't execute one of the tests:

checking for bhyve... /usr/local/sbin/bhyve
checking for bhyvectl... /usr/local/sbin/bhyvectl
checking for bhyveload... /usr/local/sbin/bhyveload
./configure: line 62602: test: too many arguments

Fix the shell statement testing the 3 binaries.

m4/virt-driver-bhyve.m4

@@ -28,7 +28,7 @@ AC_DEFUN([LIBVIRT_DRIVER_CHECK_BHYVE],[
         AC_PATH_PROG([BHYVECTL], [bhyvectl], [], [$PATH:/usr/sbin])
         AC_PATH_PROG([BHYVELOAD], [bhyveload], [], [$PATH:/usr/sbin/])
 
-        if test -z "$BHYVE" || test -z "$BHYVECTL" \
+        if test -z "$BHYVE" || test -z "$BHYVECTL" || \
             test -z "$BHYVELOAD" || test "$with_freebsd" = "no"; then
             if test "$with_bhyve" = "check"; then
                 with_bhyve="no"