Support for booting without initramfs

Previously when initramfs-* was not found in a deployment's
boot directory, it was assumed that rootfs is prepared for
ostree booting by a kernel patch.

With this patch, the behaviour changes to be - if initramfs-*
is not found, assume that system is using a static
ostree-prepare-root as init process. Booting without initramfs
is a common use case on embedded systems. This approach is
also more convenient, than having to patch the kernel.

Closes: #1401
Approved by: cgwalters

src/boot/grub2/ostree-grub-generator

@@ -28,7 +28,7 @@ entries_path=$(dirname $new_grub2_cfg)/entries
 
 read_config()
 {
-    config_file=${entries_path}/${1}
+    config_file=${1}
     title=""
     initrd=""
     options=""
@@ -67,11 +67,13 @@ populate_menu()
     else
         boot_prefix="${OSTREE_BOOT_PARTITION}"
     fi
-    for config in $(ls ${entries_path}); do
+    for config in $(ls $entries_path/*.conf); do
         read_config ${config}
         menu="${menu}menuentry '${title}' {\n"
         menu="${menu}\t linux ${boot_prefix}${linux} ${options}\n"
-        menu="${menu}\t initrd ${boot_prefix}${initrd}\n"
+        if [ -n "${initrd}" ] ; then
+            menu="${menu}\t initrd ${boot_prefix}${initrd}\n"
+        fi
         menu="${menu}}\n\n"
     done
     # The printf command seems to be more reliable across shells for special character (\n, \t) evaluation