Fix uniqueness check of initrd in fedora-minimal

The check suffered from various flaws.

First, due to missing quotes around $initrd, 'wc -l' would always see
1 line no matter how many results the find returned.

Second, echo adds a line break making 'wc -l' count 1 even for empty
string. We need to add a check for empty string.

Change-Id: Ib2c67960f566dbdc471d9585a4cef1beb1cc38ab
Closes-Bug: #1506692

elements/fedora-minimal/install.d/99-ramdisk

@@ -9,7 +9,7 @@ set -o pipefail
 initrd=$(find /boot -name initrd)
 kernel_version=$(rpm -qa | grep kernel | sort | head -n 1 | cut -d '-' -f 2,3)
 
-if [ "$(echo $initrd | wc -l)" -eq 1 ]; then
+if [ -n "$initrd" -a $(echo "$initrd" | wc -l) -eq 1 ]; then
     cp $initrd /boot/initrd-$kernel_version.img
 else
     echo "Zero or multiple initrds found. This should not happen."