conjure-up bug 'Could not determine LXD version'

The current `snap` flavors of `conjure-up`:

```bash
drpaneas@ubuntu1704:~$ sudo snap info conjure-up
name:      conjure-up
summary:   "Package runtime for conjure-up spells"
publisher: canonical
contact:   https://github.com/conjure-up/conjure-up
description: |
  This package provides conjure-up, an interface to installing spells that
  provide the user with an end to end walkthrough experience for installing and
  using big software.

channels:
  latest/stable:    2.2.0                    (453) 88MB classic
  latest/candidate: 2.2.1-20170619.2006      (461) 92MB classic
  latest/beta:      2.2.0                    (432) 88MB classic
  latest/edge:      2.3-alpha1-20170619.1906 (460) 92MB classic
```

I am going to install the latest one, which in that context, I mean *2.3-alpha1-20170619.1906*.

```bash
drpaneas@ubuntu1704:~$ sudo snap install conjure-up --edge
error: This revision of snap "conjure-up" was published using classic confinement and thus may perform
       arbitrary system changes outside of the security sandbox that snaps are usually confined to, which
       may put your system at risk.

       If you understand and want to proceed repeat the command including --classic.
```

Well, I am pretty *OK* with ignoring this *warning*, so let's roll the dice:

```bash
drpaneas@ubuntu1704:~$ sudo snap install conjure-up --edge --classic
2017-06-20T00:14:07+02:00 INFO cannot auto connect core:core-support-plug to core:core-support: (slot auto-connection), existing connection state "core:core-support-plug core:core-support" in the way
2017-06-20T00:14:07+02:00 INFO Waiting for restart...
2017-06-20T00:14:07+02:00 INFO cannot auto connect core:core-support-plug to core:core-support: (slot auto-connection), existing connection state "core:core-support-plug core:core-support" in the way
conjure-up (edge) 2.3-alpha1-20170619.1906 from 'canonical' installed
```

So, as you can see, I've got it installed, along with *core*:

```bash
drpaneas@ubuntu1704:~$ sudo snap list
Name        Version                   Rev   Developer  Notes
conjure-up  2.3-alpha1-20170619.1906  460   canonical  classic
core        16-2                      1689  canonical  -
```

Now let's try to run it:

```bash
drpaneas@ubuntu1704:~$ conjure-up
Traceback (most recent call last):
  File "/snap/conjure-up/460/bin/conjure-up", line 11, in <module>
    load_entry_point('conjure-up==2.3a1', 'console_scripts', 'conjure-up')()
  File "/snap/conjure-up/460/lib/python3.6/site-packages/conjureup/app.py", line 241, in main
    utils.lxd_version(),
  File "/snap/conjure-up/460/lib/python3.6/site-packages/conjureup/utils.py", line 205, in lxd_version
    raise Exception("Could not determine LXD version.")
Exception: Could not determine LXD version.
```

As you can see, it complains about not able to determine the LXD version -- which actually makes sense because I don't even have LXD installed in my machine:

```bash
drpaneas@ubuntu1704:~$ dpkg-query -L lxd
dpkg-query: package 'lxd' is not installed
```