CC-3573: Use posix_geteuid instead of "whoami" to detect who is running PHP script

-done

install_minimal/airtime-uninstall

@@ -1,7 +1,7 @@
 #!/bin/bash
 
 #Check if root user
-if [ `whoami` != 'root' ]; then
+if [[ $EUID -ne 0 ]]; then
     echo "Please run as root user."
     exit 1
 fi