Add a gate-specific tox env for functional tests

The functional gate jobs (*-neutron-dsvm-functional) need special
configuration (e.g. OS_SUDO_TESTING, OS_ROOTWRAP_CMD) to run tests.
This patch adds a new gate-specific tox env (tox -e dsvm-functional)
that sets the appropriate values and allows easy duplication of the
results of the upstream job on a host that has successfully run
devstack with neutron enabled.

A new configuration option, OS_FAIL_ON_MISSING_DEPS, is also set by
the dsvm-functional tox env to ensure that dependency failures will
result in failures rather than skips when run in the gate.

Change-Id: Idbfef1ba72ed129a3021509c7969e2685b8a6d09
Partial-bug: #1336172
Dnsmasq config files syntax issue when dhcp_domain is empty

When using dhcp-agent with the following property dhcp_domain=""
addn_hosts and host files genererated for Dnsmasq have wrong syntax
concerning hostname parameter (dot char at the end).

As described in RFC-952 the hostname grammar is as follows:
<hname> ::= <name>*["."<name>]
<name>  ::= <let>[*[<let-or-digit-or-hyphen>]<let-or-digit>]
Hence it can't be conclude with a dot char.

Dnsmasq process is waiting for a hostname (2nd parameter) in the
following files:
"addn_hosts" file contains:
   20.0.0.3 host-20-0-0-3. host-20-0-0-3
"host" file contains:
   fa:16:3e:bf:e1:e4,host-20-0-0-3.,20.0.0.3

With the patch you will get:
"addn_hosts":
   20.0.0.3 host-20-0-0-3 host-20-0-0-3
"host":
   fa:16:3e:bf:e1:e4,host-20-0-0-3,20.0.0.3

Change-Id: I4c10169019becaed6b2968b74f03ef356244a057
Closes-Bug: #1326256
Merge "Dnsmasq config files syntax issue when dhcp_domain is empty"
Merge "Add a gate-specific tox env for functional tests"