virt-manager does not recognize dynamically created brdige devices that do not have ifcfg files

Issue

• The bridge devices on the server are not listed in the combo box of available source devices for NIC congiuration section in Details tab of the virt-manager.
• Note that we do not use network configuration files, e.g., ifcfg-eth, in /etc/sysconfig/network-scripts Instead, the interfaces are created as below:

 /bin/echo +bond0 > /sys/class/net/bonding_masters 
 /bin/echo active-backup > /sys/class/net/bond0/bonding/mode
 /bin/echo 100 > /sys/class/net/bond0/bonding/miimon 
 /bin/echo +eth0 > /sys/class/net/bond0/bonding/slaves
 /bin/echo +eth2 > /sys/class/net/bond0/bonding/slaves
 /sbin/ip link set bond0 up
 /usr/sbin/brctl addbr br_bond0
 /usr/sbin/brctl addif br_bond0 bond0
 /sbin/ip link set br_bond0 up