Reduce vexxhost to 10 server
We are still seeing a large number of gate jobs timing out on
vexxhost.  Reduce down to 10 servers, until we can properly audit the
failures.
Currently the gate for tripleo change queue has reset 4 times today on
slow compute nodes.
@@ -981,7 +981,7 @@ providers:
cloud: vexxhost
api-timeout: 60
boot-timeout: 120
- max-servers: 20
+ max-servers: 10
rate: 0.001
image-type: raw
template-hostname: '{image.name}-{timestamp}'
