Billing issues have cleared on the org - taking a stab at this.

First attempt: let's get a Linux CI going.

This changes does the following:
- Moves the broadcast to be only before the master reconfiguration to both before *and* after - a fix following 88dcf0c to fix the gap.
- Tweaks tests by overall lessening runtime (and thus build server time). Overall, fixes a few static timeouts to be conditional (so they short circuit faster if met), and brings some tests that were some variant of the above into RELEASE since they're safe now.
- Changes `UntilCondition` to take a `TimeSpan`, just because clearer. Even though I IntelliSense completed `.FromMinutes()` earlier and watched it like an idiot for a while...I stand by this decision!
- Locks the `ITestOutputHelper` writer because...that was jacked up in races:

![off to the races](https://user-images.githubusercontent.com/454813/77232395-2f799980-6b77-11ea-8fb4-0398de25e313.png)

------

Note: a lot of the test changes are just optimizations to delays which allow longer but short-circuit sooner. The important changes are in broadcast and locking around the test runner. I can think of downsides to neither, but want some @mgravell eyes. This should resolve a lot of flaky-ness with local (and build agent) tests. Not all of it, but a lot of it!

Old message:
> To create a disconnected multiplexer, disable AbortOnConnectFail.

New message proposal:
> Error connecting right now. To allow this multiplexer to continue retrying until it's able to connect, use abortConnect=false in your connection string or AbortOnConnectFail=false; in your code.

* ConnectionMultiplexer: track global counts for deebugging

* Build dammit

* Move to per-multiplexer/add tests

Note: I know mutiplexer isn't spelled right - will fix that in a follow-up to avoid noise.

* Fix test key names

Broken since the 2.1 bump, oops

* Simplify the NoConnectionAvailable static

Simpifies usage for all callers. Also shares code and adds diagnostics to the "no connection" case.

* Add tests for NoConnectionException

* Failover: fix tests and debug some

SubscriptionsSurviveMasterSwitchAsync is a thorn in our side - moving to DEBUG.

* Remove bad check

Inner is irrelevant here - can be not-null depending on the connection race.

* Update message and add more tests!

* Bump pipelines to 2.1.6

* fix naming of SentinelGetSentinelAddressesAsync

* tyop

* Sentinel: don't use async over sync with .Result

Co-authored-by: mgravell <marc.gravell@gmail.com>

We were throwing in event handlers...that's not good. Also post-thread sleep in timer callbacks.

* Including SslProtocols in ConfigurationOptions.ToString()

* Removing an unnecessary method and making the code concise (based on code review comments)

Co-authored-by: Sampath Vuyyuru <sampath.vuyyuru@kincentric.com>

…cation (redis 6)

fix build to get green shields for Source Link and Deterministic