salt.module.smartos_imgadm now supports vacuum

[sjorge]

Working my way through issue #25986, added vacuum support to remove unused images.

Slowly getting more familiar with salt modules, first time returning data in a nice dict.
Wouldn't hurt to give it a quick extra sanity check.

[root@core ~]# salt-call --local imgadm.vacuum True
[INFO    ] Executing command '/usr/sbin/imgadm vacuum -f' in directory '/root'
local:
    ----------
    a79dc83a-e3a7-11e4-bfe5-d3bb86399352:
        ----------
        name:
            lx-centos-6
        version:
            20150415
    d5b3865c-0804-11e5-be21-dbc4ce844ddc:
        ----------
        name:
            lx-centos-6
        version:
            20150601

[root@core ~]# salt-call --local imgadm.vacuum
[INFO    ] Executing command '/usr/sbin/imgadm vacuum -f' in directory '/root'
local:
    - d5b3865c-0804-11e5-be21-dbc4ce844ddc

[sjorge]

Superseded by PR #26145, closing this one.