Add note about Linux Bridge MTU Bug w/ VXLAN tun

There's a horrible hard-to-diagnose bug when using vxlan tunelling.

This patch adds a note including the simple workaround.

Change-Id: I20a8ec46a91c7ffe1533338de5968d1b83badb6f
Closes-Bug: 1242534
Publish training-guides publicly

Add training-guides link to doc.openstack.org web sites and to
the support appendix.

Update local-files.html to follow the change.

Change-Id: I09f26e0c6f102efc37f7c2028a369567b5b43be7
Merge "Publish training-guides publicly"
Merge "Add note about Linux Bridge MTU Bug w/ VXLAN tun"