improve warning message of space checking

For core_collector like makedumpfile use case, it will compress and filter the
vmcore so free space small than memtotal is mostly ok. But we can not guarantee
it will be always ok.

The "there is not enough space" is not accurate, improve it to "there might be
not enough space"

Signed-off-by: Dave Young <dyoung@redhat.com>
Acked-by: Vivek Goyal <vgoyal@redhat.com>

mkdumprd

@@ -123,8 +123,8 @@ check_size() {
     esac
 
     if [ $avail -lt $memtotal ]; then
-        echo "Warning: There is not enough space to save a vmcore."
-        echo "         The size of $2 should be much greater than $memtotal kilo bytes."
+        echo "Warning: There might not be enough space to save a vmcore."
+        echo "         The size of $2 should be greater than $memtotal kilo bytes."
     fi
 }