fix(ssh): update host autocompletion

The current completion doesn't work correctly when there are multiple hosts
per line, e.g.:

```
Host foo bar baz
  ...
```

SSH config also allows to have repeated hosts, e.g.:

```
Host foo bar
  ...

Host foo
  ...
```

With this commit we split all the host values in lines, sort them out and then
make a unique array of them.

plugins/ssh/ssh.plugin.zsh

@@ -4,9 +4,16 @@
 # Filter out wildcard host sections.
 _ssh_configfile="$HOME/.ssh/config"
 if [[ -f "$_ssh_configfile" ]]; then
-  _hosts=($(egrep '^Host.*' "$_ssh_configfile" | awk '{print $2}' | grep -v '^*' | sed -e 's/\.*\*$//'))
-  zstyle ':completion:*:hosts' hosts $_hosts
-  unset _hosts
+  _ssh_hosts=($(
+    egrep '^Host.*' "$_ssh_configfile" |\
+    awk '{for (i=2; i<=NF; i++) print $i}' |\
+    sort |\
+    uniq |\
+    grep -v '^*' |\
+    sed -e 's/\.*\*$//'
+  ))
+  zstyle ':completion:*:hosts' hosts $_ssh_hosts
+  unset _ssh_hosts
 fi
 unset _ssh_configfile