In Python3.7 async is a keyword [1]
In Python3.7 async is a keyword [1]

Change all instances of "async" to "async_"

[1] https://docs.python.org/3/whatsnew/3.7.html

Change-Id: Ib4121d72e97da2f35adb83b257fa8775370e21df

openstack/monasca-api,openstack/monasca-api,stackforge/monasca-api,openstack/monasca-api,stackforge/monasca-api,stackforge/monasca-api,stackforge/monasca-api