lsinird: Adding option "-m|--mod" to list dracut modules in the image

lsinird: Adding option "-m|--mod" to list dracut modules in the image

This patch adds option "-m|--mod" to lsinitrd to list dracut
modules in the image  because sometimes  having an option to
only list the dracut modules in the image could be handy.

Sample output:
--------------

[hbathini@localhost dracut]$ sudo ./lsinitrd.sh initramfs-3.11.10-100.fc18.x86_64.img -m
Image: initramfs-3.11.10-100.fc18.x86_64.img: 33M
========================================================================
Version: dracut-029-1.fc18.2

dracut modules:
i18n
network
ifcfg
drm
plymouth
btrfs
crypt
dm
dmraid
kernel-modules
lvm
mdraid
cifs
iscsi
nfs
resume
rootfs-block
terminfo
udev-rules
biosdevname
systemd
usrmount
base
fs-lib
shutdown
========================================================================

Signed-off-by: Hari Bathini <hbathini@linux.vnet.ibm.com>