Fix flaky testSetAll

[219sansim]

Motivation:

Problem
The testSetAll unit test checks output of MultiMap which compares output of MultiMap and unintentionally checks for the order of the elements of output of MultiMap.toString() method. This may cause the following tests to sometimes fail even though the code under test may be working as expected -

io.vertx.core.http.headers.CaseInsensitiveHeadersTest#testSetAll
io.vertx.core.http.headers.VertxHttpHeadersTest#testSetAll

Solution
The solution is to check for both possible orderings of MultiMap which may be outputs of toString() method

Reproduction of Bug

Setup the NonDex tool and run

mvn edu.illinois:nondex-maven-plugin:2.1.1:nondex -Dtest=io.vertx.core.http.headers.CaseInsensitiveHeadersTest#testSetAll -DnondexRuns=10
mvn edu.illinois:nondex-maven-plugin:2.1.1:nondex -Dtest=io.vertx.core.http.headers.VertxHttpHeadersTest#testSetAll -DnondexRuns=10

Error Message

Tests run: 84, Failures: 2, Errors: 0, Skipped: 0, Time elapsed: 0.007 sec <<< FAILURE! - in io.vertx.core.http.headers.CaseInsensitiveHeadersTest
testSetAll(io.vertx.core.http.headers.CaseInsensitiveHeadersTest)  Time elapsed: 0.001 sec  <<< FAILURE!
org.junit.ComparisonFailure: expected:<[=
aaa=bbb]
> but was:<[aaa=bbb
=]
>