core: inherit kernelopts from the template by default

Fixes qubesos/qubes-issues#1091

core-modules/000QubesVm.py

@@ -146,6 +146,7 @@ class QubesVm(object):
                 "order": 31,
                 "func": lambda value: value if not self.uses_default_kernelopts\
                     else defaults["kernelopts_pcidevs"] if len(self.pcidevs)>0 \
+                    else self.template.kernelopts if self.template
                     else defaults["kernelopts"] },
             "mac": { "attr": "_mac", "default": None },
             "include_in_backups": {

doc/qvm-tools/qvm-prefs.rst

@@ -111,8 +111,10 @@ kernelopts
     VM kernel parameters (available only for PV VMs). This can be used to
     workaround some hardware specific problems (eg for NetVM). Setting to
     ``default`` will use some reasonable defaults (currently different for VMs
-    with PCI devices and without). Some helpful options (for debugging
-    purposes): ``earlyprintk=xen``, ``init=/bin/bash``
+    with PCI devices and without). For VM without PCI devices
+    ``default`` option means inherit this value from the VM template (if any).
+    Some helpful options (for debugging purposes): ``earlyprintk=xen``,
+    ``init=/bin/bash``
 
 name
     Accepted values: alphanumerical name