migrate tests to using current sk8s sample functions

[jldec]

building and running the current samples should make the test less vulnerable to changes in how samples are built and run, and it would exercise more user-facing (OSS) code.

[freynca]

• System tests currently use an outdated sample function (https://github.com/pivotal-cf/pfs-ci/tree/master/integration/sample_functions/java/uppercase)
• Will switch to using the Greeter sample from sk8s (https://github.com/markfisher/sk8s/tree/master/samples/java/greeter)

[markfisher]

@freynca there is nothing out-of-date about that sample function

the POM doesn't need to edit the manifest, but the Function itself should run as-is

we do need to align on the way we build function containers, e.g.: https://github.com/markfisher/sk8s/blob/master/samples/java/greeter/Dockerfile

I do think it's probably a good idea to have the sample-test use greeter instead, but I wanted to clarify that the uppercase Function itself would still be compatible if accompanied by the Dockerfile as expected by the shell-based CLI as in the various sample READMEs here: https://github.com/markfisher/sk8s/tree/master/samples

[markfisher]

I created these 2 issues which I think should help us align on the container expectations: https://github.com/markfisher/sk8s/issues/142 https://github.com/markfisher/sk8s/issues/143

[freynca]

Closing as redundant. System tests now using samples from projectriff/riff