Update Mask async calls as synchronous.policy.xml

[KrisFrost]

This is not for long running requests. Request taking 4+ minutes can experience forced timeounts in a cloud environment where devices such as a load balancer have hard coded connection timeouts. For scenarios running more than seconds, make sure the client is involved to keep the connection alive.

[KrisFrost]

Updating comments to reflect long running request can result in connection timeouts

[adrianhall]

Closing for age.