Add hypervisor_type option

In general, Tempest sends a request to Nova without any specific host
in most tests for booting a server, and Nova selects a valid host.
However some tests specify a host and this option is a hint to select
the host on heterogeneous compute environment.

Closes-Bug: #1611683

Change-Id: Ic15de7be1000c82bc13517f0bc5cf20d5248873b
diff --git a/tempest/config.py b/tempest/config.py
index bc9215c..3d61461 100644
--- a/tempest/config.py
+++ b/tempest/config.py
@@ -278,6 +278,11 @@
                      'be utilized by some multinode specific tests to ensure '
                      'that requests match the expected size of the cluster '
                      'you are testing with.')),
+    cfg.StrOpt('hypervisor_type',
+               default=None,
+               help="Hypervisor type of the test target on heterogeneous "
+                    "compute environment. The value can be 'QEMU', 'xen' or "
+                    "something."),
     cfg.StrOpt('min_microversion',
                default=None,
                help="Lower version of the test target microversion range. "