virt: Make virsh absence non fatal for other tests

This is a solution for issue autotest#563.

If one is only testing kvm components, for example,
the absence of virsh should not be relevant, but
since the module throws an exception on import, and
module is imported on env_processing, a ValueError
will be thrown and fail completely all the tests.

Let's fail things only when actual functionality of
the module is called, during the initialization of
the BaseVirsh class.

CC: Chris Evich <[email protected]>
Signed-off-by: Lucas Meneghel Rodrigues <[email protected]>

client/tests/virt/virttest/virsh.py

@@ -38,7 +38,11 @@
 ]
 
 # default virsh executable
-VIRSH_EXEC = os_dep.command("virsh")
+try:
+    VIRSH_EXEC = os_dep.command("virsh")
+except ValueError:
+    VIRSH_EXEC = None
+    logging.info("Command 'virsh' is not installed, please install it")
 
 # Virsh class properties and default values
 # Schema: {<name>:<default>}
@@ -97,6 +101,9 @@ def __init__(self, **dargs):
         """
         Initialize libvirt connection/state from VIRSH_PROPERTIES and/or dargs
         """
+        if VIRSH_EXEC is None:
+            raise ValueError("Command 'virsh' is not installed, "
+                             "please install it.")
         # Setup defaults, (calls properties)
         _dargs = VIRSH_PROPERTIES.copy()
         _dargs.update(dargs)