Splitting guestagent code

Changes:
 - git-subtree-dir: guestagent
 - git-subtree-mainline: 2daad86fa934f3b76df1ec8be44dcbab86550d83
 - git-subtree-split: bccfefdc0ef7ec3b7f2096156592b7418417ef8e

Implements: blueprint separate-guestagent-related-code
Change-Id: I28d8a3e4a7d81b5092ec35cbf4acae1f63526485