Fix capitalization in Security Guide

Change-Id: I861da5aa8cf4eba2c785f6bdc9979e4994624dd6
Closes-Bug: #1253834
Configure metadata source for cloud-init

When building Ubuntu images the metadata source to be used by
cloud-initmust be explicitly set.

Change-Id: I30e3336cf65f8c1baed358efd78d90cde1d0cc02
Closes-Bug: #1250881
backport: havana
Merge "Fix capitalization in Security Guide"
Merge "Configure metadata source for cloud-init"