Aggregate object should be "grouping of compute hosts"

The describe of Compute "aggregate" in command-objects and commands
documents use "a grouping of servers", but exactly that should be a
grouping of compute hosts. "server" object in OSC is a virtual machine
instance, and server group should be "grouping of servers".

Change-Id: Ib034fed15f11fc3e756985b3131a9922129ed6bf
Closes-Bug: #1563172
Related-Bug: #1542171

Author: kiwik

doc/source/command-objects/aggregate.rst

@@ -2,7 +2,7 @@
 aggregate
 =========
 
-Server aggregates provide a mechanism to group servers according to certain
+Host aggregates provide a mechanism to group hosts according to certain
 criteria.
 
 Compute v2

doc/source/commands.rst

@@ -71,7 +71,7 @@ referring to both Compute and Volume quotas.
 
 * ``access token``: (**Identity**) long-lived OAuth-based token
 * ``availability zone``: (**Compute**, **Network**, **Volume**) a logical partition of hosts or block storage or network services
-* ``aggregate``: (**Compute**) a grouping of servers
+* ``aggregate``: (**Compute**) a grouping of compute hosts
 * ``backup``: (**Volume**) a volume copy
 * ``catalog``: (**Identity**) service catalog
 * ``command``: (**Internal**) installed commands in the OSC process