Can't run server tests with Tox on Trusty

[Caio Begotti]

Seems, as confirmed by Barry on IRC, generated envs are not available in tox-1.6.x, the version available on Trusty.

caio1982@ubuntuair:~/Devel/PES/sis-newwork/server$ tox
Traceback (most recent call last):
  File "/usr/bin/tox", line 9, in <module>
    load_entry_point('tox==1.6.0', 'console_scripts', 'tox')()
  File "/usr/lib/python2.7/dist-packages/tox/_cmdline.py", line 25, in main
    config = parseconfig(args, 'tox')
  File "/usr/lib/python2.7/dist-packages/tox/_config.py", line 44, in parseconfig
    parseini(config, inipath)
  File "/usr/lib/python2.7/dist-packages/tox/_config.py", line 241, in __init__
    config.envlist = self._getenvlist(reader, toxsection)
  File "/usr/lib/python2.7/dist-packages/tox/_config.py", line 343, in _getenvlist
    envlist = reader.getlist(toxsection, "envlist", sep=",")
  File "/usr/lib/python2.7/dist-packages/tox/_config.py", line 413, in getlist
    s = self.getdefault(section, name, None)
  File "/usr/lib/python2.7/dist-packages/tox/_config.py", line 511, in getdefault
    x = self._replace(x)
  File "/usr/lib/python2.7/dist-packages/tox/_config.py", line 618, in _replace
    return rexpattern.sub(replace_func, x)
  File "/usr/lib/python2.7/dist-packages/tox/_config.py", line 609, in _replace_match_no_quote
    return self._replace_match(match, quote=False)
  File "/usr/lib/python2.7/dist-packages/tox/_config.py", line 604, in _replace_match
    return handler(match, quote)
  File "/usr/lib/python2.7/dist-packages/tox/_config.py", line 567, in _replace_substitution
    val = self._substitute_from_other_section(sub_key, quote)
  File "/usr/lib/python2.7/dist-packages/tox/_config.py", line 561, in _substitute_from_other_section
    "substitution key %r not found" % key)
tox.ConfigError: ConfigError: substitution key 'py27,py34' not found