[Event Hubs Client] Initial Migration

Project Structure
  - Solution and projects adapated to central engineering system structure,
    format, and conventions

  - Target platforms updated to conform to the central engineering system.  For
    this initial effort, the Xamarin.iOS10 target has been converted to
    netstandard1.4, which is compatible with the previously configured iOS verison.

  - Target platforms have been updated to only include uap10.0 on Windows and when a flag is passed
    to indicate that MsBuild is being used, as UWP currently cannot be build from .NET core.  In the
    current configuration for the engineering system, this means that the uap10.0 target will not be
    built; discussions for adding support have begun.

        NOTE: This is subject to change pending the outcome of discussions with the engineering team
        on the best way to enable support within the build system.

  - Updated conditional compilation to recognize netstandard1.4 and uap10.0 as the target platforms
    for consumers which the Identity Model for Active Directory package does not support
    client certificate use; the constructs previously hidden for iOS and UWP are now
    hidden for netstandard1.4 and UWP.

  - Forced a target platform of x64 for Service Fabric Processor and Test projects,
    due to the restrictions imposed by the Service Fabric library references.

  - Configured overrides to the engineering system default assembly signing key, to
    allow for use of the existing Azure Messaging key while the client library is in Track 1,
    to avoid breaking changes.

  - Normalized and updated package references to known-good versions used by the centralized
    SDKs and attempted to remove fragmentation between target platform references.

Azure Resource Templates
  - Converted values which are assumed by the test infrastructure from parameters to variables
    with the expected names.  This ensures that deployment is compatible with the test suite without
    a user needing to have awareness of the expected names.

ReadMe
  - Restructured and updated content to snap to the Azure SDK repository ReadMe template, as closely
    as possible for a Track 1 migration.

Event Hubs Tests
  - Designated tests that interact with Azure services as "Live" tests, allowing them to be filtered when
    Azure environments are not available or when it is desirable to run only fast, self-contained tests, such
    as build verification for pull requests.

  - Moved hardcoded values tied to Azure resources into the TestConstants file, so that well-known
    and assumed values are centrally located.

  - Updated the approach for reading environment variables to a lazy approach instead of in a static
    constructor, allowing tests that do not use Azure resoruces to make use of TestUtility functionality
    without the need for a set of "Live" environment variables.

  - Moved test utility and infrastructure classes to a dedcated folder for better organization and in
    anticipation of additional test infrastructure additions during the upcoming test stabilization.

  - Added configuration for the XUnit test runner to enable diagnostics output and in anticipation of
    parallelization of the tests during stabilization work.

  - Added access modifiers to tests in order to satisfy code analysis rules for unused private members.

  - Small fixes to async patterns in some tests, to await rather than returning the task directly, per
    XUnit recommended practices.

  - Small additions to failure messages, to grant additional context and highlight actual vs expected values.

  - Temporarily set some unstable tests in the the ServiceFabricProcessor area to be skipped
    until for the initial migration; to be investiated and stablized as part of issue Azure#5451.