lxd: select server based on name from result

[thp-canonical]

Due to prefix or regular expression matching, lxd list may list multiple instances. To account for that, instead of assuming it will always return a slice where the first item is the one we're interested in, iterate over the result and pick the one that matches the name exactly. Return an error If no such match exists.

According to lxd documentation, the argument to the list command can be:

• A prefix of the instance name
• A regular expression on the instance name
• A key/value pair referring to a configuration item
• A key/value pair with a shorthand key
• A regular expression matching a config item

[ZeyadYasser]

LGTM, Thank you!

[niemeyer]

We might just format the name so it does match exactly, but that seems fine too.

[niemeyer]

Thanks @thp-canonical and @cmatsuoka.