Adds alarm time constraint support to ceilometer CLI

Time constraints can be specified for create and update
families of commands with the following format:

--time-constraint name=constraint1;start='0 11 * * *';duration=300

This switch can be specified multiple times in the case of
multiple time constraints.

With update commands, time constraints are updated by name,
e.g. --time-constraint name=constraint1;duration=500 updates
the constraint 'constraint1' with a new duration 500.

Time constraints can be removed with update commands using the
switch --remove-time-constraint=constraint1,constraint2 .

Example of display outputs:

> ceilometer alarm-list
+--------------------------------------+-------+-------------------+---------+------------+----------------------------+--------------------------------------------------------------+
| Alarm ID                             | Name  | State             | Enabled | Continuous | Alarm condition            | Time constraints                                             |
+--------------------------------------+-------+-------------------+---------+------------+----------------------------+--------------------------------------------------------------+
| 2ead776d-2fc7-47a2-b0bb-0f88dcefa457 | test2 | insufficient data | True    | False      | cpu == 50.0 during 1 x 60s | cons1 at 0 11 * * *  for 300s, cons2 at 0 23 * * *  for 600s |
+--------------------------------------+-------+-------------------+---------+------------+----------------------------+--------------------------------------------------------------+

> ceilometer alarm-show -a
+---------------------------+-----------------------------------------------------------------------+
| Property                  | Value                                                                 |
+---------------------------+-----------------------------------------------------------------------+
| alarm_actions             | []                                                                    |
| alarm_id                  | 2ead776d-2fc7-47a2-b0bb-0f88dcefa457                                  |
| comparison_operator       | eq                                                                    |
| description               | Alarm when cpu is eq a avg of 50.0 over 60 seconds                    |
| enabled                   | True                                                                  |
| evaluation_periods        | 1                                                                     |
| exclude_outliers          | False                                                                 |
| insufficient_data_actions | []                                                                    |
| meter_name                | cpu                                                                   |
| name                      | test2                                                                 |
| ok_actions                | []                                                                    |
| period                    | 60                                                                    |
| project_id                | 962f75ad22c24cbf99d40d7b82718505                                      |
| query                     |                                                                       |
| repeat_actions            | False                                                                 |
| state                     | insufficient data                                                     |
| statistic                 | avg                                                                   |
| threshold                 | 50.0                                                                  |
| time_constraints          | [{name: cons1,                                                        |
|                           |   description: Time constraint at 0 11 * * * lasting for 300 seconds, |
|                           |   start: 0 11 * * *,                                                  |
|                           |   duration: 300},                                                     |
|                           |  {name: cons2,                                                        |
|                           |   description: Time constraint at 0 23 * * * lasting for 600 seconds, |
|                           |   start: 0 23 * * *,                                                  |
|                           |   duration: 600}]                                                     |
| type                      | threshold                                                             |
| user_id                   | 76f335df8e2f4c7e9e8185e26ea85759                                      |
+---------------------------+-----------------------------------------------------------------------+

> ceilometer alarm-history -a 2ead776d-2fc7-47a2-b0bb-0f88dcefa457
+----------+----------------------------+--------------------------------------------------------------------------------+
| Type     | Timestamp                  | Detail                                                                         |
+----------+----------------------------+--------------------------------------------------------------------------------+
| creation | 2014-03-06T07:41:35.362050 | name: test2                                                                    |
|          |                            | description: Alarm when cpu is eq a avg of 50.0 over 60 seconds                |
|          |                            | type: threshold                                                                |
|          |                            | rule: cpu == 50.0 during 1 x 60s                                               |
|          |                            | time_constraints: cons1 at 0 11 * * *  for 300s, cons2 at 0 23 * * *  for 600s |
+----------+----------------------------+--------------------------------------------------------------------------------+

Change-Id: I3953276537b4526e46e5e6d229d6fa154f8ab0fc
Closes-Bug: #1288246
Merge "Adds alarm time constraint support to ceilometer CLI"
Implementation of statistics aggregators

This corresponds to do API calls on:
/v2/meters/meter-name/statistics?aggregate.func=func-name

Usage:
aggregates = [{'func': 'cardinality', 'param': 'resource_id'}])
client.statistics.list(meter_name="instance", aggregates=aggregates)

CLI:
ceilometer statistics -m instance -a "cardinality<-resource_id"

Change-Id: I0096668585a5c7e7985973f07049eb91f44413fe