fix(network,dbus): improve dependency checking

Decouple implementation details of the backend
dependencies from the meta module.

Call check_module for each submodule instead
of reimplementing sub-package dependencies
inside the meta module itself.

Add missing NetworkManager binary to the
network-manager dracut module check.

modules.d/09dbus/module-setup.sh

@@ -19,7 +19,7 @@ depends() {
         fi
     done
 
-    if find_binary dbus-broker &> /dev/null; then
+    if check_module "dbus-broker"; then
         echo "dbus-broker"
         return 0
     else

modules.d/35network-manager/module-setup.sh

@@ -2,7 +2,7 @@
 
 # called by dracut
 check() {
-    require_binaries sed grep || return 1
+    require_binaries sed grep NetworkManager || return 1
 
     # do not add this module by default
     return 255

modules.d/40network/module-setup.sh

@@ -17,11 +17,11 @@ depends() {
     done
 
     if [ -z "$network_handler" ]; then
-        if [[ -e $dracutsysrootdir$systemdsystemunitdir/connman.service ]]; then
+        if check_module "connman"; then
             network_handler="connman"
-        elif [[ -x $dracutsysrootdir/usr/libexec/nm-initrd-generator ]] || [[ -x $dracutsysrootdir/usr/lib/nm-initrd-generator ]]; then
+        elif check_module "network-manager"; then
             network_handler="network-manager"
-        elif [[ -x $dracutsysrootdir$systemdutildir/systemd-networkd ]]; then
+        elif check_module "systemd-networkd"; then
             network_handler="systemd-networkd"
         else
             network_handler="network-legacy"