Avoid changing default endpoint fixes #346

[jvrsantacruz]

When an alternative lxd server is installed via snap, pylxd will change the default to it, effectively
switching from the current server to a different one without the user knowing.

This was making the default value of the Client unreliable as it might change anytime without warning.

Applications relying on the default value of the endpoint for the Client had to be forced now to set LXD_DIR to avoid sudden changes when users get a side installation to play with.

[codecov-io]

Codecov Report

Merging #347 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #347      +/-   ##
==========================================
+ Coverage   96.83%   96.83%   +<.01%     
==========================================
  Files          12       12              
  Lines         980      981       +1     
  Branches      110      110              
==========================================
+ Hits          949      950       +1     
  Misses         12       12              
  Partials       19       19

Impacted Files	Coverage Δ
pylxd/client.py	98.7% <100%> (ø)	⬆️

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[ajkavanagh]

I'm sorry, but the choose the snap version needs to stay. There is merit in a conversation about whether to check for the /var/lib/lxd/unix.socket first, and defaulting to that, rather than the snap, but the pylxd library will fail to work in a snap only installed lxd environment which is the default in 18.10 and above (on Ubuntu).

[jvrsantacruz]

Hi,

Thanks for reviewing this. I wasn't aware that the snap installation was about to be the single one.
As to this date we used it to install alternative or modern versions and test.

I rewrote the previous commit to look for /var/lib/lxd/unix.socket before going for /var/snap/lxd/common/lxd/unix.socket. If that's more in line with what's expected of the library.

Thank you!

[ajkavanagh]

Thanks for the update; I'm reviewing and testing this. I think it's probably okay to include this functionality, but I need to check that it works after an lxd.migrate.

[ajkavanagh]

This looks good, and my testing against pkg and snap versions is fine. Thanks for the changes.