Uses None instead of mutables for function param defaults

Addressing bug 1307878, changes use of mutable lists and dicts as
default arguments and defaults them within the function. Otherwise,
those defaults can be unexpectedly persisted with the function between
invocations and erupt into mass hysteria on the streets.

To my knowledge there aren't known cases of the current use causing
specific issues, but needs addressing (even stylistically) to avoid
problems in the future -- ones that may crop up as extremely subtle or
intermittent bugs...or worse, security vulnerabilities.

In Glance's case there are ACL-related methods using this, so
although I haven't confirmed one way or the other yet, I've marked it
with SecurityImpact so that a more knowledgeable set of eyes can
review it in this context as well.

Closes-Bug: #1307878
SecurityImpact

Change-Id: Ic17c330eff701ff63701c0029b26db7093a1d73d
Fixes "bad format" in replicator for valid hosts

Due to a bad regex, the glance-replicator tool rejects any source or
target host:port combination that contains a period. As a result, only
hostnames without periods can be used.

This fix expands the host/port checks to:
  - allow periods in hostnames
  - allow and verify IPv6 addr/port pairs (i.e., [fe80::f00d:face]:1234)
  - allow and verify IPv4 addr/port pairs (i.e., 172.17.17.2:1234)
  - sanity-check port numbers

This also includes extensive tests for each component of the parsing,
and adds network_utils to openstack-common.conf.

Change-Id: I94fdd7a57a4cb0aa5d79f66d68be159d1f1266d1
Closes-Bug: #1216247
Merge "Uses None instead of mutables for function param defaults"
Merge "Fixes "bad format" in replicator for valid hosts"
WIP: simple non-running task eventlet executor

partially implements bp async-glance-workers

Change-Id: I382472fffd0fdad43573e72b2e78a9a6ed1e1f1a