VLAN Trunking: Added skipped state for RHEL/CentOS 6.6 and lower
VLAN Trunking: Added skipped state for RHEL/CentOS 6.6 and lower

We will now skip VLAN Trunking TC on RHEL/CentOS 6.6 and lower because
the feature is unsupported

bogdancarpusor/lis-test,chvalean/lis-test,ampintilie/lis-test,ilenghel/lis-test,mihaico/lis-test,chvalean/lis-test,adriansuhov/lis-test,adriansuhov/lis-test,bogdancarpusor/lis-test,LIS/lis-test,ilenghel/lis-test,HuijingHei/lis-test,ilenghel/lis-test,chvalean/lis-test,chvalean/lis-test,HuijingHei/lis-test,mihaico/lis-test,bogdancarpusor/lis-test,ampintilie/lis-test,lixuemin2016/lis-test,senugala/lis-test,ilenghel/lis-test,LIS/lis-test,adriansuhov/lis-test,LIS/lis-test,adriansuhov/lis-test,ampintilie/lis-test,HuijingHei/lis-test,ampintilie/lis-test,senugala/lis-test,mihaico/lis-test,LIS/lis-test,HuijingHei/lis-test,senugala/lis-test,lixuemin2016/lis-test,lixuemin2016/lis-test,lixuemin2016/lis-test