uvt-kvm create --memory 1024 --ephemeral-disk 8 dualb
superMkhb:/home/khb>uvt-kvm wait dualb
superMkhb:/home/khb>uvt-kvm ssh dualb
Welcome to Ubuntu 18.04.2 LTS (GNU/Linux 4.15.0-48-generic x86_64)

 * Documentation:  https://help.ubuntu.com
 * Management:     https://landscape.canonical.com
 * Support:        https://ubuntu.com/advantage

  System information as of Mon Apr 29 15:39:16 UTC 2019

  System load:  0.11              Processes:           84
  Usage of /:   12.8% of 7.58GB   Users logged in:     0
  Memory usage: 12%               IP address for ens3: 192.168.122.93
...


superMkhb:/home/khb>virsh shutdown dualb
Domain dualb is being shutdown

superMkhb:/home/khb>virsh attach-interface --domain dualb --type network --source maas --config 
Interface attached successfully

superMkhb:/home/khb>virsh start dualb
Domain dualb started

superMkhb:/home/khb>uvt-kvm wait dualb
uvt-kvm: error: libvirt domain 'dualb' has more than one NIC defined.

Interestingly, today doing it as originally written (and experienced) isn't failing this way. That is,
superMkhb:/home/khb>uvt-kvm destroy dualb
superMkhb:/home/khb>uvt-kvm create --memory 1024 --ephemeral-disk 8 dualb
superMkhb:/home/khb>uvt-kvm wait dualb
superMkhb:/home/khb>uvt-kvm ssh dualb
Welcome to Ubuntu 18.04.2 LTS (GNU/Linux 4.15.0-48-generic x86_64)

 * Documentation:  https://help.ubuntu.com
 * Management:     https://landscape.canonical.com
 * Support:        https://ubuntu.com/advantage

  System information as of Mon Apr 29 15:45:04 UTC 2019

  System load:  0.13              Processes:           83
  Usage of /:   12.8% of 7.58GB   Users logged in:     0
  Memory usage: 12%               IP address for ens3: 192.168.122.215
  Swap usage:   0%

ubuntu@dualb:~$ exit
logout
Connection to 192.168.122.215 closed.
superMkhb:/home/khb>virsh attach-interface --domain dualb --type network --source maas --config --live
Interface attached successfully

superMkhb:/home/khb>uvt-kvm ssh dualb
Welcome to Ubuntu 18.04.2 LTS (GNU/Linux 4.15.0-48-generic x86_64)

 * Documentation:  https://help.ubuntu.com
 * Management:     https://landscape.canonical.com
 * Support:        https://ubuntu.com/advantage

  System information as of Mon Apr 29 15:45:18 UTC 2019

  System load:  0.1               Processes:           83
  Usage of /:   12.8% of 7.58GB   Users logged in:     0
  Memory usage: 12%               IP address for ens3: 192.168.122.215
  Swap usage:   0%


0 packages can be updated.
0 updates are security updates.


Last login: Mon Apr 29 15:45:05 2019 from 192.168.122.1
To run a command as administrator (user "root"), use "sudo <command>".
See "man sudo_root" for details.

ubuntu@dualb:~$ ifconfig -a
ens3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.168.122.215  netmask 255.255.255.0  broadcast 192.168.122.255
        inet6 fe80::5054:ff:fe6f:d48b  prefixlen 64  scopeid 0x20<link>
        ether 52:54:00:6f:d4:8b  txqueuelen 1000  (Ethernet)
        RX packets 618  bytes 510393 (510.3 KB)
        RX errors 0  dropped 82  overruns 0  frame 0
        TX packets 357  bytes 41278 (41.2 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

ens8: flags=4098<BROADCAST,MULTICAST>  mtu 1500
        ether 52:54:00:df:aa:50  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0