Don't use root_helper when it's not needed

LinuxBridge agent doesn't need to use root_helper when checking if
a device exists. Root priviledges are required to perform operations
inside a namespace and it's not the case here.

Change-Id: I12e0cde2f4dd3b3f8e7f5ed9e90e2805a4466aaa
Closes-bug: #1305800
ofagent: move main module from ryu repository

the recent oslo.messaging transition broke ofagent.
this commit fixes the regression.

historically the main module of ofagent has been maintained
in ryu's repository.  this commit moves it into neutron's
repository and add common_config.init() call which is necesary
for the new rpc code.

Closes-Bug: #1332478
Change-Id: Icf215b20cd84ef44b51439e55b1815d72041ba3f
Merge multiple constants defining linux interface maximum length

DEVICE_NAME_MAX_LEN constant in neutron.common.constants replaces
and correct multiple constants defining linux interface maximum
length.

Closes-Bug: #1332571
Change-Id: I63f760a21e17dcd57b3685b1e71c913d2722e097
Moved rpc_compat.py code back into rpc.py

Most of this code will probably stay with us for quite some time, so
let's make things easier and consider them as our way of doing RPC.

blueprint oslo-messaging

Change-Id: Iaf353b23f9c54b82d1e02a6bd5a5960cec827c88
don't ignore rules that are already enforced

H302 / H304 are clean in the neutron source tree, so it seems
like they shouldn't be ignored. This requires no code changes to
enable.

If there is a longer standing reason for these ignores, would be
great to document in tox.ini.

Change-Id: Ib0f483e4f8fbd328815775a2a6f58be448172bd9
Merge "Don't use root_helper when it's not needed"
Merge "don't ignore rules that are already enforced"
Merge "Moved rpc_compat.py code back into rpc.py"
Merge "Merge multiple constants defining linux interface maximum length"
Merge "ofagent: move main module from ryu repository"