Add dependency on handlers role to docker role

[langston-barrett]

• Installs cleanly on a fresh build of most recent master branch
• Upgrades cleanly from the most recent release
• Updates documentation relevant to the changes

Useful if you run the Docker role by itself. Fixes this issue:

TASK: [docker | systemd drop-in for options] ********************************** 
ok: [lb0-worker-003] => (item=10-options.conf)
ok: [lb0-worker-001] => (item=10-options.conf)
ok: [lb0-kubeworker-002] => (item=10-options.conf)
ok: [lb0-worker-004] => (item=10-options.conf)
ok: [lb0-worker-002] => (item=10-options.conf)
ok: [lb0-kubeworker-001] => (item=10-options.conf)
ok: [lb0-edge-01] => (item=10-options.conf)
ok: [lb0-control-03] => (item=10-options.conf)
ok: [lb0-control-02] => (item=10-options.conf)
ok: [lb0-control-01] => (item=10-options.conf)
changed: [lb0-worker-003] => (item=12-network-options.conf)
changed: [lb0-worker-004] => (item=12-network-options.conf)
changed: [lb0-worker-001] => (item=12-network-options.conf)
changed: [lb0-worker-002] => (item=12-network-options.conf)
changed: [lb0-kubeworker-001] => (item=12-network-options.conf)
changed: [lb0-kubeworker-002] => (item=12-network-options.conf)
changed: [lb0-edge-01] => (item=12-network-options.conf)
changed: [lb0-control-01] => (item=12-network-options.conf)
changed: [lb0-control-03] => (item=12-network-options.conf)
changed: [lb0-control-02] => (item=12-network-options.conf)
ERROR: change handler (reload systemd) is not defined

[ryane]

lgtm, tested on aws