Introduce StripExpectHeader filter and a property to control it.

Some providers (specifically HP Cloud and Google Cloud Storage) do not
properly support Expect: 100-continue headers. JDK7 is stricter in its
handling of the Expect header than JDK6 -- in particular, it expects
servers to properly respond to an expect header and times out only if a
prior timeout did not exist on the underlying HTTP connection. As a
result, JDK7 tests against these providers hang and fail.

This commit introduces a new filter -- appropriate called
StripExpectHeader -- that is controlled by the property
jclouds.strip-expect-header. The property defaults to false to preserve
existing behavior but allows applications to tweak Expect header
handling.

Tested by running HPCS live tests with JDK7 -- previously most of these
tests would fail with timeouts.

Closes JCLOUDS-181