fix empty stdin from request

in some requests the stdin channel can be attached to request data
if the request data is empty the channel local path was unpopulated which lead to HTTP 400
this patch will populate the local path for `stdin` with `/dev/null` in such case (this is a standard behavior for CGI)
fixes issue #152
Merge pull request #153 from pkit/bug_fix

fix empty stdin from request
proxyquery: dont directly import cache_from_env

Directly importing functions makes it difficult/impossible to mock
things in tests.
proxyquery: config_path is an instance var

In RestController, `config_path` was declared as a class variable. It is
not. It is an instance variable.
proxyquery: add docstring to `load_config`

This adds parameter docs to RestController.load_config.
proxyquery: fix a premature return in RestController

Fixes a caching-related 500 error in RestController.

RestController.load_config was returning too early if the
`cluster_config` was retrieved from memcached. Later in the
controller call chain, if `cluster_config` is set, `config_path` is
expected to be set as well, but the `load_config` call was returning
prematurely before `config_path` could be set.

This was resulting in intermittent generic 500 errors when exercising
the /api/ URL REST features. (Basically, a reqest would work the first
time, then throw errors until the cache expires--about 60 seconds
later--and then start working again.)
proxyquery: fix premature return in ApiController

ApiController.load_config was returning too early if the
`cluster_config` was retrieved from memcached. Later in the controller
call chain, if `cluster_config` is set, `config_path` is expected to be
set as well, but the `load_config` call was returning prematurely before
`config_path` could be set.

This was resulting in intermittent generic 500 errors when exercising
the /api/ URL REST features. (Basically, a reqest would work the first
time, then throw errors until the cache expires--about 60 seconds
later--and then start working again.)