fix: improve systemd detection to check if systemd is actually running

The previous implementation checked if systemctl command exists, but this
fails in container environments where systemctl is installed but systemd
is not running as PID 1. This caused the script to try using systemctl
commands which would fail with 'System has not been booted with systemd'.

Now we check for /run/systemd/system directory which only exists when
systemd is actually running as the init system.

Signed-off-by: Gajesh Bhat <gajeshbht@gmail.com>

Author: gajeshbhat

install.sh

@@ -300,7 +300,11 @@ get_distribution() {
 # Check if systemd is available and running
 # Returns 0 if systemd is available, 1 otherwise
 has_systemd() {
-	command_exists systemctl && systemctl --version >/dev/null 2>&1
+	if [ -d /run/systemd/system ]; then
+		return 0
+	else
+		return 1
+	fi
 }
 
 # Start and enable Docker daemon service after installation