Remove invalid hints from Properties inputs.

[ehoner]

Validate contents of Properties object used for "hints". This is related to an issue (error below) reported by clients after deploying #117. The expected use of the "hints" and "pipeline" options are unchanged. The unit test validate the following conditions:

1. An empty "hints" map is ignored.
2. Non-empty "hints" are valid as either key value pairs or flags.
3. Parsing of "pipeline" occurs regardless of "hints" (no collision detection).

---

The input Properties parameter for parseHints included a "hints" key with an empty value.

Caused by: java.lang.IllegalArgumentException: Chunk [] is not a valid entry
        at com.google.common.base.Preconditions.checkArgument(Preconditions.java:218) ~[com.google.guava.guava-33.3.1-jre.jar:?]
        at com.google.common.base.Splitter$MapSplitter.split(Splitter.java:523) ~[com.google.guava.guava-33.3.1-jre.jar:?]
        at com.linkedin.hoptimator.util.DeploymentService.parseHints(DeploymentService.java:100) ~[com.linkedin.hoptimator.hoptimator-util-0.0.37-alpha.jar:?]
        at com.linkedin.hoptimator.util.DeploymentService.plan(DeploymentService.java:90) ~[com.linkedin.hoptimator.hoptimator-util-0.0.37-alpha.jar:?]
...