blkfront: add uevent for size change

linux-aws test kernel with the patch applied: http://kernel.ubuntu.com/~kamal/lp1683878/

I performed this test in EC2:

- Launched an instance of latest Xenial AMI in us-west-1 (ami-2afbde4a, kernel 4.4.0-1013-aws) with 8GB root EBS volume
- Created a second EBS volume, 100GB, and attached as /dev/sdf.
- Ran sudo udevadm monitor --kernel --udev and resized both volumes. No udev events were registered.

I repeated the test with the test kernel in comment #1 (4.4.0-1016-aws). Upon resizing both volumes, this output was captured:
KERNEL[100.355617] change /devices/vbd-768/block/xvda (block)
UDEV [100.373979] change /devices/vbd-768/block/xvda (block)
KERNEL[127.255821] change /devices/vbd-51792/block/xvdf (block)
UDEV [127.269313] change /devices/vbd-51792/block/xvdf (block)

The volume modifications were causing udev events to be emitted.

This bug was fixed in the package linux-aws - 4.4.0-1016.25

---------------
linux-aws (4.4.0-1016.25) xenial; urgency=low

  * linux-aws: 4.4.0-1016.25 -proposed tracker (LP: #1684458)

  * blkfront: add uevent for size change (LP: #1683878)
    - SAUCE: blkfront: add uevent for size change

  [ Ubuntu: 4.4.0-75.96 ]

  * linux: 4.4.0-75.96 -proposed tracker (LP: #1684441)
  * [Hyper-V] hv: util: move waiting for release to hv_utils_transport itself
    (LP: #1682561)
    - Drivers: hv: util: move waiting for release to hv_utils_transport itself

linux-aws (4.4.0-1015.24) xenial; urgency=low

  * linux-aws: 4.4.0-1015.24 -proposed tracker (LP: #1682047)

  [ Ubuntu: 4.4.0-74.95 ]

  * linux: 4.4.0-74.95 -proposed tracker (LP: #1682041)
  * [Hyper-V] hv: vmbus: Raise retry/wait limits in vmbus_post_msg()
    (LP: #1681893)
    - Drivers: hv: vmbus: Raise retry/wait limits in vmbus_post_msg()

linux-aws (4.4.0-1014.23) xenial; urgency=low

  * linux-aws: 4.4.0-1014.23 -proposed tracker (LP: #1680424)

  [ Ubuntu: 4.4.0-73.94 ]

  * linux: 4.4.0-73.94 -proposed tracker (LP: #1680416)
  * CVE-2017-6353
    - sctp: deny peeloff operation on asocs with threads sleeping on it
  * vfat: missing iso8859-1 charset (LP: #1677230)
    - [Config] NLS_ISO8859_1=y
  * Regression: KVM modules should be on main kernel package (LP: #1678099)
    - [Config] powerpc: Add kvm-hv and kvm-pr to the generic inclusion list
  * linux-lts-xenial 4.4.0-63.84~14.04.2 ADT test failure with linux-lts-xenial
    4.4.0-63.84~14.04.2 (LP: #1664912)
    - SAUCE: apparmor: fix link auditing failure due to, uninitialized var
  * regession tests failing after stackprofile test is run (LP: #1661030)
    - SAUCE: fix regression with domain change in complain mode
  * Permission denied and inconsistent behavior in complain mode with 'ip netns
    list' command (LP: #1648903)
    - SAUCE: fix regression with domain change in complain mode
  * unexpected errno=13 and disconnected path when trying to open /proc/1/ns/mnt
    from a unshared mount namespace (LP: #1656121)
    - SAUCE: apparmor: null profiles should inherit parent control flags
  * apparmor refcount leak of profile namespace when removing profiles
    (LP: #1660849)
    - SAUCE: apparmor: fix ns ref count link when removing profiles from policy
  * tor in lxd: apparmor="DENIED" operation="change_onexec"
    namespace="root//CONTAINERNAME_<var-lib-lxd>" profile="unconfined"
    name="system_tor" (LP: #1648143)
    - SAUCE: apparmor: Fix no_new_privs blocking change_onexec when using stacked
      namespaces
  * apparmor oops in bind_mnt when dev_path lookup fails (LP: #1660840)
    - SAUCE: apparmor: fix oops in bind_mnt when dev_path lookup fails
  * apparmor auditing denied access of special apparmor .null fi\ le
    (LP: #1660836)
    - SAUCE: apparmor: Don't audit denied access of special apparmor .null file
  * apparmor label leak when new label is unused (LP: #1660834)
    - SAUCE: apparmor: fix label leak when new label is unused
  * apparmor reference count bug in label_merge_insert() (LP: #1660833)
    - SAUCE: apparmor: fix reference count bug in label_merge_insert()
  * apparmor's raw_data file in securityfs ...