Escape command substitutions in %post

Not escaping these causes expansion at kickstart time and the directory
names are hardcoded within the built image.
Merge pull request #7 from dcarley/escape_mktemp

Escape command substitutions in %post
Merge pull request #8 from dcarley/label_rootfs

Use FS labels for the root filesystem
Add more modules

Based on patch from Andy Grimm <agrimm@gmail.com>
Stop listing ephemeral disks explicitly

Ephemeral disks aren't always set up for images and vary widely
across instance types.  Let's not try to mount them from here
Add a command line option to extract kernel(s) and ramdisk(s)
add modules for vmware support
Remove code that's no longer used
add sym53c8xx and sd_mod for non-virtio use case
add example CentOS 6 config
Fix epel url
Set bootloader option to "fix" device names

Xen device names in EL6.1+ got changed from what you would
reasonably expect (https://bugzilla.redhat.com/show_bug.cgi?id=729586)
and then to get back to the right thing, you have to pass an
option to the module.  Go for sanity.
Switch to ext4 for el6
Use cloud-init to handle user key setup

cloud-init is kind of odd but is generally the "expected" thing
at this point so we might as well use it instead of doing the
ssh key stuff ourself.  And it defaults to ec2-user, so we
need that user + having that user in sudoers
Merge with upstream, removing some device mapping hackery