aws: fix path resolution of aws completion for Ubuntu (#7812)

plugins/aws/aws.plugin.zsh

@@ -67,11 +67,18 @@ _awscli-homebrew-installed() {
 # get aws_zsh_completer.sh location from $PATH
 _aws_zsh_completer_path="$commands[aws_zsh_completer.sh]"
 
-# otherwise check if installed via Homebrew
-if [[ -z $_aws_zsh_completer_path ]] && _awscli-homebrew-installed; then
-  _aws_zsh_completer_path=$_brew_prefix/libexec/bin/aws_zsh_completer.sh
-else
-  _aws_zsh_completer_path=/usr/share/zsh/site-functions/aws_zsh_completer.sh
+# otherwise check common locations
+if [[ -z $_aws_zsh_completer_path ]]; then
+  # Homebrew
+  if _awscli-homebrew-installed; then
+    _aws_zsh_completer_path=$_brew_prefix/libexec/bin/aws_zsh_completer.sh
+  # Ubuntu
+  elif [[ -e /usr/share/zsh/vendor-completions/_awscli ]]; then
+    _aws_zsh_completer_path=/usr/share/zsh/vendor-completions/_awscli
+  # RPM
+  else
+    _aws_zsh_completer_path=/usr/share/zsh/site-functions/aws_zsh_completer.sh
+  fi
 fi
 
 [[ -r $_aws_zsh_completer_path ]] && source $_aws_zsh_completer_path