packet.ospf: workaround a bytearray vs buffer problem

feeding bytearray to struct.unpack() crashes on some environment.
(depends on the interpreter versions?  i'm not sure.)

this fixes the following crash in the unit test.
the crash was seen on travis-ci, too.
https://travis-ci.org/osrg/ryu/jobs/15578909
https://s3.amazonaws.com/archive.travis-ci.org/jobs/15578909/log.txt

======================================================================
ERROR: test_hello (packet.test_ospf.Test_ospf)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/yamamoto/git/ryu/ryu/tests/unit/packet/test_ospf.py", line 68, in test_hello
    msg2, cls, rest = ospf.OSPFMessage.parser(binmsg)
  File "/Users/yamamoto/git/ryu/ryu/lib/packet/ospf.py", line 443, in parser
    kwargs = subcls.parser(binmsg)
  File "/Users/yamamoto/git/ryu/ryu/lib/packet/ospf.py", line 501, in parser
    n = addrconv.ipv4.bin_to_text(n)
  File "/Users/yamamoto/git/ryu/ryu/lib/addrconv.py", line 30, in bin_to_text
    return str(self._addr(self._strat.packed_to_int(bin),
  File "/Users/yamamoto/git/ryu/.venv/lib/python2.7/site-packages/netaddr/strategy/ipv4.py", line 196, in packed_to_int
    return _struct.unpack('>I', packed_int)[0]
error: unpack requires a string argument of length 4

----------------------------------------------------------------------

Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
requires lxml

will be used for OF-Config stuff.
add some convenient OF-Config classes

some python classes for a set of OF-Config 1.1.1 types.

the goal is to allow programmers use OF-Config without direct
XML manipulations.
of_config.capable_switch: api tweak

tweak method to take of_config.classes classes instead of xml.
tests.integrated.test_of_config: update after capable_switch api change
of_config.capable_switch: add delete_config and copy_config
a simple of-config client command

the placement (ryu/tests/bin) was suggested by FUJITA Tomonori.
of_config_cli: add delete_config and copy_config
of_config_cli: add add_queue command

totally untested as i have no access to switches which support
the operation.
of_config: allows both of of-config element names and python style names

for convenience of api consumers, allows both of of-config style
element names (eg. logical-switches) and python style attribute
names (eg. logical_switches).
of_config_cli: remove no longer necessary "_pythonify" stuff