Copyright updates.

Address some memory hazards in Cython code

Remove binary tags, restrict tag characters to ASCII

Fix sanity test for C#'s 'build_packages.bat.template'

Windows C# distribtests

Package protoc artifacts for all platforms in Grpc.Tools nuget

Stress test scripts to launch in GKE

Some __dealloc__ methods were calling Python methods, and some
references were being dropped on the floor instead of threaded through
gRPC core.

Allow new credential types to be added to tests.

Added a test to verify user agent prefix can be set correctly.

tools/gke directies and instead create tools/gcp). Move scripts around
in to the appropriate directories

tools/gke directies and instead create tools/gcp). Move scripts around
in to the appropriate directories

Explicitly delete node_modules directory after running tests on Windows

Don't fail when generating report.xml on gcc4.4 

Pollset & pollset-set implementation firewalls

everything configurable

Fix fedora20 python distribtest

Fix ruby distribtest on centos6

Fix python distribtest on fedora20 and fedora21.