tests: memcache: fix regex
tests: memcache: fix regex

Some versions of python do not tolerate this regex:

   r'(\w*)?'

ERROR: test_incr (__main__.TestCommands)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "tests/memcached/test_memcached.py", line 464, in test_incr
    self.assertRegexpMatches(call('incr key 1\r\n').decode(), r'0(\w*)?\r\n')
  File "/usr/lib64/python3.3/unittest/case.py", line 1178, in deprecated_func
    return original_func(*args, **kwargs)
  File "/usr/lib64/python3.3/unittest/case.py", line 1153, in assertRegex
    expected_regex = re.compile(expected_regex)
  File "/usr/lib64/python3.3/re.py", line 214, in compile
    return _compile(pattern, flags)
  File "/usr/lib64/python3.3/re.py", line 281, in _compile
    p = sre_compile.compile(pattern, flags)
  File "/usr/lib64/python3.3/sre_compile.py", line 498, in compile
    code = _code(p, flags)
  File "/usr/lib64/python3.3/sre_compile.py", line 483, in _code
    _compile(code, p.data, flags)
  File "/usr/lib64/python3.3/sre_compile.py", line 75, in _compile
    elif _simple(av) and op is not REPEAT:
  File "/usr/lib64/python3.3/sre_compile.py", line 362, in _simple
    raise error("nothing to repeat")
sre_constants.error: nothing to repeat

hongliangzhao/seastar,chunshengster/seastar,joerg84/seastar,kjniemi/scylla,wildinto/scylla,xtao/seastar,phonkee/scylla,raphaelsc/scylla,tempbottle/scylla,cloudius-systems/seastar,asias/scylla,kangkot/scylla,acbellini/scylla,koolhazz/seastar,wildinto/seastar,linearregression/seastar,dreamsxin/seastar,sjperkins/seastar,duarten/scylla,mixja/seastar,cloudius-systems/seastar,rluta/scylla,dwdm/seastar,joerg84/seastar,kjniemi/scylla,avikivity/scylla,wildinto/seastar,duarten/scylla,tempbottle/seastar,eklitzke/scylla,dwdm/scylla,ducthangho/imdb,dwdm/seastar,bzero/seastar,aruanruan/scylla,shyamalschandra/seastar,avikivity/seastar,kjniemi/seastar,capturePointer/scylla,scylladb/scylla-seastar,glommer/scylla,scylladb/scylla,scylladb/scylla,acbellini/scylla,dwdm/seastar,gwicke/scylla,scylladb/scylla-seastar,glommer/scylla,avikivity/seastar,respu/scylla,norcimo5/seastar,justintung/scylla,rentongzhang/scylla,victorbriz/scylla,shyamalschandra/seastar,printedheart/seastar,anzihenry/seastar,scylladb/scylla,scylladb/scylla-seastar,stamhe/scylla,flashbuckets/seastar,hongliangzhao/seastar,dwdm/scylla,bowlofstew/seastar,victorbriz/scylla,slivne/seastar,scylladb/seastar,shaunstanislaus/scylla,leejir/seastar,koolhazz/seastar,syuu1228/seastar,joerg84/seastar,guiquanz/scylla,mixja/seastar,avikivity/scylla,rentongzhang/scylla,chunshengster/seastar,stamhe/scylla,raphaelsc/seastar,jonathanleang/seastar,linearregression/scylla,tempbottle/scylla,sjperkins/seastar,norcimo5/seastar,anzihenry/seastar,printedheart/seastar,acbellini/scylla,syuu1228/seastar,xtao/seastar,anzihenry/seastar,printedheart/seastar,capturePointer/scylla,chunshengster/seastar,justintung/scylla,linearregression/seastar,stamhe/scylla,guiquanz/scylla,capturePointer/scylla,leejir/seastar,raphaelsc/scylla,stamhe/seastar,wildinto/seastar,bowlofstew/seastar,aruanruan/scylla,norcimo5/seastar,scylladb/scylla,acbellini/seastar,kjniemi/seastar,rentongzhang/scylla,raphaelsc/scylla,dwdm/scylla,senseb/scylla,tempbottle/scylla,eklitzke/scylla,slivne/seastar,dreamsxin/seastar,cloudius-systems/seastar,guiquanz/scylla,kjniemi/seastar,asias/scylla,xtao/seastar,bowlofstew/scylla,respu/scylla,gwicke/scylla,rluta/scylla,gwicke/scylla,linearregression/seastar,linearregression/scylla,bowlofstew/seastar,respu/scylla,aruanruan/scylla,koolhazz/seastar,shyamalschandra/seastar,raphaelsc/seastar,flashbuckets/seastar,avikivity/seastar,phonkee/scylla,rluta/scylla,jonathanleang/seastar,wildinto/scylla,victorbriz/scylla,acbellini/seastar,bowlofstew/scylla,senseb/scylla,slivne/seastar,syuu1228/seastar,eklitzke/scylla,bzero/seastar,kjniemi/scylla,ducthangho/imdb,bzero/seastar,leejir/seastar,scylladb/seastar,raphaelsc/seastar,asias/scylla,avikivity/scylla,shaunstanislaus/scylla,phonkee/scylla,dreamsxin/seastar,duarten/scylla,mixja/seastar,bowlofstew/scylla,tempbottle/seastar,stamhe/seastar,stamhe/seastar,justintung/scylla,tempbottle/seastar,jonathanleang/seastar,shaunstanislaus/scylla,glommer/scylla,senseb/scylla,kangkot/scylla,scylladb/seastar,kangkot/scylla,linearregression/scylla,hongliangzhao/seastar,ducthangho/imdb,acbellini/seastar,flashbuckets/seastar,wildinto/scylla,sjperkins/seastar