Return system stats from get state

[#60787050]

Signed-off-by: Zac Clark <zclark@pivotallabs.com>
Use sigar for system stats (not monit)

Signed-off-by: Zac Clark <zclark@pivotallabs.com>
Update get_state tests to assert on json

[#60787050]

Signed-off-by: Zac Clark <zclark@pivotallabs.com>
Added basic disk stats to get_state with full

[#60787050]

Signed-off-by: Zac Clark <zclark@pivotallabs.com>
Cleaned up get_state

- ensure vitals are not in the JSON if not asking for full

[#60787050]

Signed-off-by: Zac Clark <zclark@pivotallabs.com>
Use Percentage type for stats

[#60787050]

Signed-off-by: Zac Clark <zclark@pivotallabs.com>
Refactored generation of vitals
- Extracted from get_state action
- Extracted from heartbeat

[#60787050]

Signed-off-by: Zac Clark <zclark@pivotallabs.com>