perf(computes): the host's info is read once per request

The overview read the host's info four times, now once (12 libvirt calls).
A connection object keeps it next to the capabilities, and the VM page and
VM stats take it from there; the VM page's cached_reads block holds only
the VM's own data. Free memory is still read each time.

vrtManager/connection.py

@@ -403,6 +403,11 @@ class wvmConnect(object):
         """The host's capabilities, read once per object (a request): most getters below parse them"""
         return self.wvm.getCapabilities()
 
+    @cached_property
+    def host_info(self):
+        """The host's info (architecture, memory in MiB, CPUs, ...), read once per object"""
+        return self.wvm.getInfo()
+
     @cached_property
     def dom_cap_xmls(self):
         """The domain capabilities read so far, by emulator, arch, machine and domain type"""