Add an option to disable cloud watch lite

This also adds a deprecation warning.
This also changes the default to use Ceilometer.

Release message:
Anyone deploying Heat should not be using OS::Heat::CWLiteAlarm, but
OS::Ceilometer::Alarm.
CWLiteAlarm should be explictly disabled in /etc/heat/heat.conf by
setting "enable_cloud_watch_lite=false". This will stop Heat from
running a period task check for alarms.

DocImpact
Change-Id: I2a10c14772bdafc001e211d7e94502ac1f6b32b1
Closes-bug: #1322128
Merge "Add an option to disable cloud watch lite"