Add a few additional useful functions

- is_*() returns True if the interface name is of a certain type
  is_bondethernet() is_loopback() is_bvi() is_bridgedomain()
  is_vxlan_tunnel() is_phy()
- get_phys() by process of elimination, returns all interface names
  that are supposed to be physical network interfaces.

Add unit tests for validator/vxlan_tunnel.py
 => Notable: while here, fix a bug in get_by_name()
Add unit tests for all the is_*() and get_phys() functions.

validator/bridgedomain.py

@@ -41,6 +41,29 @@ def get_by_name(yaml, ifname):
     return None, None
 
 
+def is_bridgedomain(yaml, ifname):
+    """ Returns True if the name is an existing bridgedomain (ie bd[0-9]+). """
+    ifname, iface = get_by_name(yaml, ifname)
+    return not iface == None
+
+
+def is_bvi(yaml, ifname):
+    """ Returns True if the interface name is an existing BVI. """
+    if not ifname.startswith("bvi"):
+        return False
+    idx = ifname[3:]
+    if not idx.isnumeric():
+        return False
+    bridgename, bridge = get_by_name(yaml, "bd%d" % (int(idx)))
+    if not bridge:
+        return False
+
+    ## If the BridgeDomain has an 'lcp', then it has a Bridge Virtual Interface
+    if 'lcp' in bridge:
+        return True
+    return False
+
+
 def get_bridge_interfaces(yaml):
     """ Returns a list of all interfaces that are bridgedomain members """