Implement passing of the destination.service details to the adapter

[guptasu]

Pass additional details to the adapter via the context object.

Adapters want to know destination service information to support multi-tenancy scenario. Mixer now passes the destination.service as part of the context object that gets delivered to the adapters via the Handler* method.

Release note:

We are now passing RequestData information inside the context object. This contains details like destination service and more in future. adapter.RequestDataFromContext methods must be used to retrieve the RequestData object from a given context.

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This change is 

[istio-testing]

@guptasu: Adding do-not-merge/release-note-label-needed because the release note process has not been followed.

One of the following labels is required "release-note", "release-note-action-required", or "release-note-none". Please see: https://github.com/kubernetes/community/blob/master/contributors/devel/pull-requests.md#write-release-notes-if-needed. Instructions for interacting with me using PR comments are available [here](https://github.com/kubernetes/community/blob/master/contributors/devel/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes/test-infra](https://github.com/kubernetes/test-infra/issues/new?title=Prow%20issue:) repository.

[douglas-reid]

/hold

[codecov[bot]]

Codecov Report

Merging #1539 into master will increase coverage by 0.04%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1539      +/-   ##
==========================================
+ Coverage   84.55%   84.59%   +0.04%     
==========================================
  Files         122      124       +2     
  Lines       11999    12012      +13     
==========================================
+ Hits        10146    10162      +16     
+ Misses       1651     1648       -3     
  Partials      202      202

Impacted Files	Coverage Δ
pkg/adapter/requestData.go	100% <100%> (ø)
pkg/runtime/dispatcher.go	96.68% <100%> (+0.01%)	:arrow_up:
pkg/runtime/requestDataBuilder.go	100% <100%> (ø)
adapter/prometheus/server.go	94.91% <0%> (+5.08%)	:arrow_up:

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[istio-testing]

@guptasu: The following test failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
prow/mixer-e2e-smoketest.sh	aa4f208fe45529516153a6de17d50d2b90186f5d	link	/test mixer-e2e-smoketest

Instructions for interacting with me using PR comments are available [here](https://github.com/kubernetes/community/blob/master/contributors/devel/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes/test-infra](https://github.com/kubernetes/test-infra/issues/new?title=Prow%20issue:) repository. I understand the commands that are listed [here](https://github.com/kubernetes/test-infra/blob/master/commands.md).

[geeknoid]

This repo is no longer accepting PRs. Please resubmit this change to the istio/istio repo.

Thanks.