Verified for xenial.  Image with cloud-init 0.7.9-48-g1c795b9-0ubuntu1~16.04.1:

2017-04-17 22:16:49,814 - cc_growpart.py[DEBUG]: No 'growpart' entry in cfg.  Using default: {'mode': 'auto', 'ignore_growroot_disabled': False, 'devices': ['/' ]}
2017-04-17 22:16:49,814 - util.py[DEBUG]: Running command ['growpart', '--help'] with allowed return codes [0] (shell=False, capture=True)
2017-04-17 22:16:49,826 - util.py[DEBUG]: Reading from /proc/1069/mountinfo (quiet=False)
2017-04-17 22:16:49,826 - util.py[DEBUG]: Read 2661 bytes from /proc/1069/mountinfo
2017-04-17 22:16:49,826 - util.py[DEBUG]: resize_devices took 0.001 seconds
2017-04-17 22:16:49,826 - cc_growpart.py[DEBUG]: '/' SKIPPED: stat of '/dev/root' failed: [Errno 2] No such file or directory: '/dev/root'
[...]
2017-04-17 22:16:49,827 - cc_resizefs.py[DEBUG]: resize_info: dev=/dev/root mnt_point=/ path=/
[...]
2017-04-17 22:16:49,832 - cc_resizefs.py[DEBUG]: Converted /dev/root to '/dev/PARTUUID=0dde3c84-01' per kernel cmdline
2017-04-17 22:16:49,832 - cc_resizefs.py[WARNING]: Device '/dev/PARTUUID=0dde3c84-01' did not exist. cannot resize: dev=/dev/root mnt_point=/ path=/


Image with cloud-init 0.7.9-90-g61eb03fe-0ubuntu1~16.04.1:

2017-04-17 22:56:47,456 - cc_growpart.py[DEBUG]: No 'growpart' entry in cfg.  Using default: {'mode': 'auto', 'ignore_growroot_disabled': False, 'devices': ['/']}
2017-04-17 22:56:47,456 - util.py[DEBUG]: Running command ['growpart', '--help'] with allowed return codes [0] (shell=False, capture=True)
2017-04-17 22:56:47,493 - util.py[DEBUG]: Reading from /proc/1064/mountinfo (quiet=False)
2017-04-17 22:56:47,493 - util.py[DEBUG]: Read 2661 bytes from /proc/1064/mountinfo
[...]
2017-04-17 22:56:47,498 - util.py[DEBUG]: Running command ['blkid', '-tPARTUUID=94eb3eec-01', '-odevice'] with allowed return codes [0, 2] (shell=False, capture=True)
2017-04-17 22:56:47,522 - util.py[DEBUG]: Reading from /sys/class/block/sda1/partition (quiet=False)
2017-04-17 22:56:47,522 - util.py[DEBUG]: Read 2 bytes from /sys/class/block/sda1/partition
2017-04-17 22:56:47,522 - util.py[DEBUG]: Reading from /sys/devices/pci0000:00/0000:00:03.0/virtio0/host0/target0:0:1/0:0:1:0/block/sda/dev (quiet=False)
2017-04-17 22:56:47,522 - util.py[DEBUG]: Read 4 bytes from /sys/devices/pci0000:00/0000:00:03.0/virtio0/host0/target0:0:1/0:0:1:0/block/sda/dev
2017-04-17 22:56:47,522 - util.py[DEBUG]: Running command ['growpart', '--dry-run', '/dev/sda', '1'] with allowed return codes [0] (shell=False, capture=True)
2017-04-17 22:56:47,731 - util.py[DEBUG]: Running command ['growpart', '/dev/sda', '1'] with allowed return codes [0] (shell=False, capture=True)
2017-04-17 22:56:47,770 - util.py[DEBUG]: resize_devices took 0.277 seconds
2017-04-17 22:56:47,770 - cc_growpart.py[INFO]: '/' resized: changed (/dev/sda, 1) from 2359296000 to 10736352768
[...]
2017-04-17 22:56:47,771 - cc_resizefs.py[DEBUG]: resize_info: dev=/dev/root mnt_point=/ path=/
[...]
2017-04-17 22:56:47,780 - util.py[DEBUG]: Running command ['blkid', '-tPARTUUID=94eb3eec-01', '-odevice'] with allowed return codes [0, 2] (shell=False, capture=True)
2017-04-17 22:56:47,794 - cc_resizefs.py[DEBUG]: Converted /dev/root to '/dev/sda1' per kernel cmdline
2017-04-17 22:56:47,794 - cc_resizefs.py[DEBUG]: Resizing / (ext4) using resize2fs /dev/sda1
2017-04-17 22:56:47,795 - util.py[DEBUG]: Running command ('resize2fs', '/dev/sda1') with allowed return codes [0] (shell=False, capture=True)
2017-04-17 22:56:47,906 - util.py[DEBUG]: Resizing took 0.111 seconds
2017-04-17 22:56:47,906 - cc_resizefs.py[DEBUG]: Resized root filesystem (type=ext4, val=True)