m1.xlarge.86 support

[johnstudarus]

The m1.xlarge.x86 systems are available in greater numbers than the c2.medium.x86 allowing more student environments to run at once. However, the m1.xlarge.x86 doesn't (by default) have a spare second drive for Rook to use.
The proposal is to strip the RAID 0 (mirrored /dev/sda and /dev/sdb) of the second drive (/dev/sdb) making the second drive available for Rook.

Commands to remove the second drive, remove the partitions and make it available for Rook to use.
mdadm /dev/md126 --fail /dev/sdb3
mdadm /dev/md126 --remove /dev/sdb3
mdadm /dev/md127 --fail /dev/sdb2
mdadm /dev/md127 --remove /dev/sdb2
wipefs -a /dev/sdb

setup/defaults/main.yml:
plan_k8s_nodes: m1.xlarge.x86

[johnstudarus]

@Miouge1 what are you thoughts on making the m1.xlarge.86 the default instead of the c2.medium.86?