test(flaky): Sorting headers for deterministic order

[mumbler6]

The order of HTTP methods in the ALLOW header (OPTIONS,PUT vs PUT,OPTIONS) is not guaranteed to be consistent in getHeaderString(), so the following test case fails if the order changes:

jersey/tests/e2e/src/test/java/org/glassfish/jersey/tests/e2e/server/wadl/NoJAXBNoWadlTest.java

Line 69 in 89de7de

public void testOptionsNoWadl() {

This PR proposes to sort the headers so that the order assumptions (in this PR, alphabetical order) in the test cases are correct.

This change was confirmed by running the NonDex tool, which explores and reports errors in different behaviors of under-determined Java APIs.

To reproduce this problem, you can run the test with NonDex using these commands:

mvn install -pl tests/e2e -am -DskipTests

mvn -pl tests/e2e edu.illinois:nondex-maven-plugin:2.1.7:nondex -Dtest=org.glassfish.jersey.tests.e2e.server.wadl.NoJAXBNoWadlTest#testOptionsNoWadl

Here are screenshots of the output produced by NonDex before and after the fix:

Please let me know if you want to discuss these changes.