Fix pypi element README.md errors

- pip install to a github URL without a git+ prefix fails.
- Need to close EOF heredoc when creating mirror.yaml

Change-Id: Ic555174881e9c06fede1cf731141cbe6eb0e0b02
Adding rhel installation element

Adding RHEL support for partitioning

RHEL 6 doesn't create /dev/loop*p* devices for partitions. It does
use device mapper to create the device under /dev/mapper/loop*p*.

This patch adds a common functioon to figure out what operating
system disk image builder is being run on, then decides where to look
for the loop partition.
This fixes an unmounting issue when building a vm on rhel.

- also allows yum update
- also unregisters from a subscription
- also removes operating system detection (uses presense of dev mapper)
Removing the -r (read-only) switch for kpartx.

- Although it's safer, -r isn't an option on a rhel host version of kpartx.