Inject TUNNEL_IDENTIFIER environment variable into build execution environment.
Introduce useGeneratedTunnelIdentifier property to control whether a tunnel identifier should be generated, exported as ENV variable, and used to identify the tunnel.

via cherry-pick of 6d020c47b
Propagate resolved options for sauce tunnel to SauceConnectStarter and SauceConnectCloser so the
tunnel-identifier is available in those contexts, during management of the tunnel.
Convert TunnelHolder to a static class whose dependencies are provided at construction time so it can be unit-tested.

The previous approach relied on the ability to access the SauceOnDemandBuilderWrapper's methods and state.
Add a unit test to verify TunnelHolder interacts with encapsulated tunnel manager when close is called.
Update ci-sauce dependency to the public SauceLabs release of v 1.72.
Enhance tunnel id generator to sanitize project names.
Relocate the useGeneratedTunnelIdentifier option and add some help describing how to use it.
Merge branch 'TRE-2149-sfly-1.X-simplify-use-of-identified-tunnels' into sfly-1.X