attribute syntax check using validvals/validrange and keywords

Ticket: CM-8101
Reviewed By: CCR-4949
Testing Done: smoke tests + ran ifup -a -s on every interface configuration file from GSS cl-supports collection

This commit is introducing ~20 keywords. The value of the different attributes
will be check against raw values and <keywords>:

'<mac>'
'<text>'
'<ipv4>'
'<ipv6>'
'<auto>': "auto"
'<ipaddr>': ipv4/6 with preflix len
'<number>'
'<interface>'
'<ipv4-vrf-text>': equivalent to: <ipv4> "vrf" <text>
'<number-ipv4-list>': example: "100=172.16.100.1 101=172.16.101.1"
'<interface-list>': example: "swp1 swp2 swp3"
'<ipv4/prefixlen>'
'<ipv6/prefixlen>'
'<ipaddr/prefixlen>'
'<number-range-list>': example: "2000 2200-3000"
'<interface-range-list>': example: "swp1=100 swp2=100" ('validrange' : ['0', '65535'])
'<mac-ipaddr/prefixlen-list>'
'<number-interface-list>': example: "4 swp1 swp2"
'<interface-yes-no-list>': example: "swp1=yes swp2=no"
'<interface-yes-no-0-1-list>'
'<interface-yes-no-auto-list>'

It's possible to combine a keyword with a range from validrange. example:
validrange: 10-50
validvals: <intrface-range-list>
value: swp1=21 swp2=42 ...

Signed-off-by: Julien Fortin <julien@cumulusnetworks.com>

addons/vlan.py

@@ -25,7 +25,7 @@ class vlan(moduleBase):
                 'attrs' : {
                         'vlan-raw-device' :
                             {'help' : 'vlan raw device',
-                             'validvals' : ['<interface>' ,]},
+                             'validvals': ['<interface>']},
                         'vlan-id' :
                             {'help' : 'vlan id',
                              'validrange' : ['0', '4096']}}}