Failing tests when building janusgraph-examples standalone

It was reported on the user list that janusgraph-examples as included in the binary distribution does not build in standalone fashion.

- Version: 0.6.0
- Link to discussed bug: https://lists.lfaidata.foundation/g/janusgraph-users/topic/88046694
- Expected Behavior: build with success
- Current Behavior: failing tests during build

Steps to Reproduce:
- unzip binary distribution
- cd examples
- mvn clean install # as prescribed in the examples/README.md

Workaround for using examples:
`mvn clean install -DskipTests`

### Stack Trace (if you have one)
-------------------------------------------------------------------------------
Test set: org.janusgraph.example.GraphAppTest
-------------------------------------------------------------------------------
Tests run: 6, Failures: 2, Errors: 0, Skipped: 0, Time elapsed: 0.832 s <<< FAILURE! - in org.janusgraph.example.GraphAppTest
openGraphConfigNotFound Time elapsed: 0.015 s <<< FAILURE!
org.opentest4j.AssertionFailedError: Unexpected exception type thrown ==> expected: but was:
at org.janusgraph.example.GraphAppTest.openGraphConfigNotFound(GraphAppTest.java:70)
Caused by: org.apache.commons.configuration2.ex.ConfigurationException: Could not locate: org.apache.commons.configuration2.io.FileLocator@439a8f59[fileName=conf/foobar,basePath=,sourceURL=,encoding=ISO-8859-1,fileSystem=,locationStrategy=]
at org.janusgraph.example.GraphAppTest.lambda$openGraphConfigNotFound$1(GraphAppTest.java:70)
at org.janusgraph.example.GraphAppTest.openGraphConfigNotFound(GraphAppTest.java:70)

openGraphNullConfig Time elapsed: 0.004 s <<< FAILURE!
org.opentest4j.AssertionFailedError: Unexpected exception type thrown ==> expected: but was:
at org.janusgraph.example.GraphAppTest.openGraphNullConfig(GraphAppTest.java:65)
Caused by: java.lang.RuntimeException: Configuration must contain a valid 'gremlin.graph' setting
at org.janusgraph.example.GraphAppTest.lambda$openGraphNullConfig$0(GraphAppTest.java:65)
at org.janusgraph.example.GraphAppTest.openGraphNullConfig(GraphAppTest.java:65)

Start in examples/README.md and reproduce with `mvn clean install` from the unpacked examples directory. Read GraphAppTest.java, especially the failing assertions at lines 65 and 70, and compare the expected exceptions with the reported configuration exceptions. Done means the standalone build passes without using `-DskipTests`.

Written by the indexing model from the issue text.