tools/qvm-ls: add --kernel option for compatibility with R3.2

There was such option on Qubes 3.2, so add it here too. This is
especially useful for kernel package - preun script use it to verify if
given kernel isn't needed anymore.

doc/manpages/qvm-ls.rst

@@ -61,6 +61,10 @@ Options
 
    Same as --format=network, for compatibility with Qubes 3.x
 
+.. option:: --kernel, -k
+
+   Same as --format=kernel, for compatibility with Qubes 3.x
+
 .. option:: --verbose, -v
 
    Increase verbosity.

qubesadmin/tools/qvm_ls.py

@@ -430,6 +430,7 @@ class Table(object):
 formats = {
     'simple': ('name', 'state', 'class', 'label', 'template', 'netvm'),
     'network': ('name', 'state', 'netvm', 'ip', 'ipback', 'gateway'),
+    'kernel': ('name', 'state', 'class', 'template', 'kernel', 'kernelopts'),
     'full': ('name', 'state', 'class', 'label', 'qid', 'xid', 'uuid'),
 #   'perf': ('name', 'state', 'cpu', 'memory'),
     'disk': ('name', 'state', 'disk',
@@ -551,6 +552,10 @@ def get_parser():
         action='store_const', dest='format', const='network',
         help='Same as --format=network')
 
+    parser.add_argument('--kernel', '-k',
+        action='store_const', dest='format', const='kernel',
+        help='Same as --format=kernel')
+
     parser.set_defaults(spinner=True)
 
 #   parser.add_argument('--conf', '-c',