Add type property to HealthMonitor in the CLI

This patch adds the missing type property which causes the Bad Request
errors when the new health monitors are posted.

This fixes MN-1582.

Signed-off-by: Taku Fukushima <tfukushima@midokura.com>
Merge pull request #141 from tfukushima/l4lb-hm-fix-v1.4

Add type property to HealthMonitor in the CLI