ovn: Rename ovn-nbd to ovn-northd.

It came up in a recent discussion that the use of 'nbd' could cause
confusion since nbd is used for "Network Block Device", which may be
used in many of the same environments that OVN would be used in.

To avoid the possible issue, just rename ovn-nbd to ovn-northd.
While we're at it, create a subdirectory under ovn/ to hold all files
related to ovn-northd.  For now it's just a single C file, but we
may add more source files in the future.

Signed-off-by: Russell Bryant <rbryant@redhat.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>

tutorial/ovs-sandbox

@@ -44,7 +44,7 @@ rungdb() {
 
 gdb_vswitchd=false
 gdb_ovsdb=false
-gdb_ovn_nbd=false
+gdb_ovn_northd=false
 gdb_ovn_controller=false
 builddir=
 srcdir=
@@ -94,7 +94,7 @@ These options force ovs-sandbox to use an installed Open vSwitch:
   -i, --installed      use installed Open vSwitch
   -g, --gdb-vswitchd   run ovs-vswitchd under gdb
   -d, --gdb-ovsdb      run ovsdb-server under gdb
-  --gdb-ovn-nbd        run ovn-nbd under gdb
+  --gdb-ovn-northd     run ovn-northd under gdb
   --gdb-ovn-controller run ovn-controller under gdb
   -S, --schema=FILE    use FILE as vswitch.ovsschema
   -o, --ovn            enable OVN
@@ -138,8 +138,8 @@ EOF
         -d|--gdb-ovsdb)
             gdb_ovsdb=true
             ;;
-        --gdb-ovn-nbd)
-            gdb_ovn_nbd=true
+        --gdb-ovn-northd)
+            gdb_ovn_northd=true
             ;;
         --gdb-ovn-controller)
             gdb_ovn_controller=true
@@ -217,7 +217,7 @@ if $built; then
     fi
     PATH=$builddir/ovsdb:$builddir/vswitchd:$builddir/utilities:$PATH
     if $ovn; then
-        PATH=$builddir/ovn:$builddir/ovn/controller:$PATH
+        PATH=$builddir/ovn:$builddir/ovn/controller:$builddir/ovn/northd:$PATH
     fi
     export PATH
 else
@@ -293,7 +293,7 @@ if $ovn; then
     ovs-vsctl set open . external-ids:ovn-encap-ip=127.0.0.1
     ovs-vsctl add-br br-int
 
-    rungdb $gdb_ovn_nbd ovn-nbd --detach --no-chdir --pidfile -vconsole:off --log-file
+    rungdb $gdb_ovn_northd ovn-northd --detach --no-chdir --pidfile -vconsole:off --log-file
     rungdb $gdb_ovn_controller ovn-controller --detach --no-chdir --pidfile -vconsole:off --log-file
 fi