Revert "kdump-lib.sh: Remove is_atomic"

Now we need this helper again, for `reset-crashkernel`

This reverts commit ff46cfb19e.

Signed-off-by: Kairui Song <kasong@redhat.com>
Acked-by: Baoquan He <bhe@redhat.com>

kdump-lib.sh

@@ -341,6 +341,11 @@ kdump_get_persistent_dev() {
     echo $(get_persistent_dev "$dev")
 }
 
+is_atomic()
+{
+    grep -q "ostree" /proc/cmdline
+}
+
 is_ipv6_address()
 {
     echo $1 | grep -q ":"