etcd data should be stored on separate block device

[Roman]

We should use separate EBS volume for etcd data, right now it's stored on root device.

core@ip-172-19-66-205 ~ $ lsblk 
NAME    MAJ:MIN RM  SIZE RO TYPE  MOUNTPOINT
xvda    202:0    0    8G  0 disk  
|-xvda6 202:6    0  128M  0 part  /usr/share/oem
|-xvda4 202:4    0    1G  0 part  
|-xvda2 202:2    0    2M  0 part  
|-xvda9 202:9    0  5.7G  0 part  /
|-xvda7 202:7    0   64M  0 part  
|-xvda3 202:3    0    1G  0 part  
| `-usr 254:0    0 1016M  1 crypt /usr
`-xvda1 202:1    0  128M  0 part  /boot
xvdb    202:16   0 37.5G  0 disk  /var/lib/docker

[xh3b4sd]

/cc @rossf7

[Ross Fairbanks]

This will be done as part of the Cloud Formation migration in giantswarm/giantswarm#2023