imvirt/vmware: don't allow output of grep on stdout

To clarify, output of virt-what executed inside a VM on a VMware cluster
is `vmware`, and `VMware ESX Server` for imvirt.

Thanks: András Korn

autoconfig.functions

@@ -185,7 +185,7 @@ VIRTUALBOX=false
 VMWARE=false
 
 if virt-what 2>/dev/null | grep -q 'vmware' || \
-  imvirt 2>/dev/null | grep -i "vmware" ; then
+  imvirt 2>/dev/null | grep -iq "vmware" ; then
   VIRTUAL=true; VMWARE=true; VIRTUAL_ENV='VMware'
 fi