Fix aggregates test with multi host setup

Fixes bug 1046222.

The aggregate exercise assumed that you have only one compute node, thus
it failed with syntax error for two hosts. With this fix, the exercise
will pick the first compute host, and use that for the tests.

Change-Id: I85d76552295d640e1a9d86fbbed781f15529d047

exercises/aggregates.sh

@@ -125,16 +125,16 @@ nova aggregate-details $AGGREGATE_ID | grep {}
 if [ "$VIRT_DRIVER" == "xenserver" ]; then
     echo "TODO(johngarbutt) add tests for add/remove host from pool aggregate"
 fi
-HOST=`nova host-list | grep compute | get_field 1`
+FIRST_HOST=`nova host-list | grep compute | get_field 1 | head -1`
 # Make sure can add two aggregates to same host
-nova aggregate-add-host $AGGREGATE_ID $HOST
-nova aggregate-add-host $AGGREGATE2_ID $HOST
-if nova aggregate-add-host $AGGREGATE2_ID $HOST; then
+nova aggregate-add-host $AGGREGATE_ID $FIRST_HOST
+nova aggregate-add-host $AGGREGATE2_ID $FIRST_HOST
+if nova aggregate-add-host $AGGREGATE2_ID $FIRST_HOST; then
     echo "ERROR could add duplicate host to single aggregate"
     exit -1
 fi
-nova aggregate-remove-host $AGGREGATE2_ID $HOST
-nova aggregate-remove-host $AGGREGATE_ID $HOST
+nova aggregate-remove-host $AGGREGATE2_ID $FIRST_HOST
+nova aggregate-remove-host $AGGREGATE_ID $FIRST_HOST
 
 # Test aggregate-delete
 # =====================