Weave through support for response attributes. (istio#402)

This does all the plumbing, but doesn't actually implement the logic
needed to produce the mixerpb.Attributes message to send to the
mixer. I'll do that next.

Expose copyBag function. (istio#414)

* Expose copyBag function.

* add comment

* Update the comment

Fix bug preventing multiple aspects from being executed for a given r…

…equest. (istio#408)

Add initial support for use of details field in rpc.Status messages. (i…

…stio#404)

* Add initial support for use of details field in rpc.Status messages.

This is the first step in addressing istio#393. It addresses the
attributes_update-related messages that are returned from Mixer.
These were the messages that had been leaking through mixerclient
out to application clients. Mixerclient will still need to figure
out how best to translate this messaging to something more
appropriate for applications to see (they should not care about
issues with attributes, etc.).

This adds support for creating BadRequest messages, which is one
of the standard rpc error types. Special handling is added for
go-multierrors (to generate a list of field violation messages).

* Fix up doc for NewBadRequest.

* Fix formatting issue with //pkg/status/BUILD.

* Add test for status.InvalidWithDetails.

* Add test for NewBadRequest.

Remove logging aspects from the testdata configuration. (istio#406)

Right now, there are problems with the logs aspects, as configured
in the testdata/ directory. As these are being relied upon to drive
configuration in demo directories, etc., this PR removes them.

When the issues with the logs bits of the configuration are resolved,
these should be added back in. This _MUST_ be verified by running mixs
and mixc and checking /metrics and seeing the logs in the output,
however.

Related to istio#403.

Major revamp of pkg/attribute. (istio#394)

- Removed all strong typing. Attribute bags now just hold a uniform map
of name/value pairs with all values being of type interface{}. It turns
out the strong typing wasn't even used anywhere except in tests.
Attribute typing is instead provided through AttributeDescriptors at a
higher level.

- Combined rootBag into mutableBag since the split was no longer useful.

- Turned the symbol MutableBag from an interface to a struct. This is so
the implementation of cross-bag functions can take advantage of implementation
details of the bag rather than just dealing with interfaces.

- Added support for merging bags, which will be used with the fork-join attribute
mutation model we'll be adding to the mixer.

Remove html tags (istio#400)

Updates for latest gogo changes in API protobufs. (istio#373)

Start plumbing in Descriptors (istio#369)

* got descriptors building, add the interface

* Add back the checked in version of cfg.pb.go generated with the script in the same dir.

* Wire in the descriptor finder to the cfg validator and manager

* push descriptors stuff down into its own package to prevent circular dep in //pkg/adapter when we go to wire things up

* remove unneeded dep

Use a tagged version of the Shared Pipeline API. (istio#357)

This will prevent changes in the libraries from breaking the builds.