auto scale: implemented scaleApplicationIfNeeded with hard coded values.

related to #154.
metrics: verify if an app has metrics enabled.

related to #154.
metrics: implemented Cpu method.

relate to #154.
metrics: get cpu metrics from graphite.

related to #154.
auto scale: added more tests for auto scale up/down.

related to #154.
auto scale: implemented method to do the auto scale.

related to #154.
auto scale: improved autoscale down test.

related to #154.
auto scale: added method to run auto scale.
Merge branch 'master' of github.com:tsuru/tsuru into autoscale
auto scale: added Action and AutoScaleConfig types.

related to #154.
auto scale: using the configured number to (in/de)create the units.

related to #154.
auto scale: implemented action.metric().

related to #154.
auto scale: implement action.operator().

related to #154.
auto scale: implemented action.value().

related to #154.
metric: implemented app.Metric().

related to #154.
auto scale: using a custom metric.

related to #154.
auto scale: removed hard coded values.

related to #154.
auto scale: improved expression regex.

related to #154.
auto scale: validate expression.

related #154.
aut scale: implement NewAction.

related to #154.