zshsrc: support hostnamectl iff hostname isn't present

The hostname binary doesn't necessarily exist, while
hostnamectl is available.

Closes: #96

etc/zsh/zshrc

@@ -837,8 +837,16 @@ function grmlcomp () {
         _ssh_hosts=()
         _etc_hosts=()
     fi
+
+    local localname
+    if check_com hostname ; then
+      localname=$(hostname)
+    elif check_com hostnamectl ; then
+      localname=$(hostnamectl --static)
+    fi
+
     hosts=(
-        $(hostname)
+        "${localname}"
         "$_ssh_config_hosts[@]"
         "$_ssh_hosts[@]"
         "$_etc_hosts[@]"
@@ -2509,8 +2517,15 @@ function grml_vcs_to_screen_title () {
 }
 
 function grml_maintain_name () {
-    # set hostname if not running on host with name 'grml'
-    if [[ -n "$HOSTNAME" ]] && [[ "$HOSTNAME" != $(hostname) ]] ; then
+    local localname
+    if check_com hostname ; then
+      localname=$(hostname)
+    elif check_com hostnamectl ; then
+      localname=$(hostnamectl --static)
+    fi
+
+    # set hostname if not running on local machine
+    if [[ -n "$HOSTNAME" ]] && [[ "$HOSTNAME" != "${localname}" ]] ; then
        NAME="@$HOSTNAME"
     fi
 }