Add a pause image for the net container.

The pause image is a 240KB image that simply pauses waiting on a signal.
Use this for the net container which only needs to act as a placeholder.
Current net image is ~2.5MB. From my tests, this reduces startup time
for the net container from ~14s to ~6s.
Add support to query kubelet's logs and cadvisor's stats through
apiserver by passing rawquery.

minor changes

Fixed a minor rebase issues.

Using ioutil.ReadAll instead of httputil.DumpResponse
comment changes
Improve test coverage for the health package and remove mocks

The current tests for the health package utilize a fake HTTP client
for testing health checks and only cover a limited set of test cases.

This patch removes the need for mocks by using the httptest package
from the standard library. After removing the fake HTTP client a bug
was found in the health.Check function; it incorrectly assumes that
a http.Response is always non-nil. Fix the issue by moving the defer
that closes the http.Response.Body after error handling.

Related tests in the registry package have be refactored to work with
the changes made to the health.Check function. All methods that implement
the health.HTTPGetInterface interface now return a http.Response with
with a noop http.Response.Body.

This patch does not introduce any changes in behavior.
Merge pull request #539 from vmarmol/pause

Add a pause image for the net container.
Merge pull request #545 from kelseyhightower/heath_tests

Improve test coverage for the health package and remove mocks
Merge pull request #457 from dchen1107/minionlogs

Add support to query kubelet's logs and cadvisor's stats through apiserver by passing rawquery
Refactor Kubelet config sources for clarity

Create a new "Pod" concept which can identify pods from
many config sources.
Switch the Kubelet to use kubelet/config

Also transfer the Kubelet from using ContainerManifest.ID to source specific
identifiers with namespacing.  Move goroutine behavior out of kubelet/ and
into integration.go and cmd/kubelet/kubelet.go for better isolation.