masakari-monitors should use os-testr instead of testr as
it is more powerful and provide much prettier output than testr.
This patch also disables the use of PY34 and adds PY35 for in tox
as the gating on python 3.4 is restricted to <= Mitaka in OpenStack.
This is due to the change from Ubuntu Trusty to Xenial, where only
python3.5 is available. Python 3 don't have 'file' builtin method so
to make it compatible with Python 2 and 3 used 'open' builtin method.
Also fixed the failing test cases due to that.
Change-Id: Ib84b0b28a845e49eaef969d0fc995b1adbb7b29d
5f59145276