Version qualifier in main response breaks testLuceneVersionConstant

[tvernum]

In #35412 we added the -SNAPSHOT qualifier to the version in the response for the main action GET /

For example:

{
  "name" : "node01",
  "cluster_name" : "elasticsearch",
  "cluster_uuid" : "E7dTpDuGR12x4qR_OOP6Rg",
  "version" : {
    "number" : "7.0.0-SNAPSHOT",
    "build_flavor" : "default",
    "build_type" : "tar",
    "build_hash" : "6964083",
    "build_date" : "2019-02-06T06:59:02.386711Z",
    "build_snapshot" : true,
    "lucene_version" : "8.0.0",
    "minimum_wire_compatibility_version" : "6.7.0",
    "minimum_index_compatibility_version" : "6.0.0-beta1"
  },
  "tagline" : "You Know, for Search"
}

In 6.x the qualifier was not included:

{
  "name" : "node01",
  "cluster_name" : "elasticsearch",
  "cluster_uuid" : "j1Cagrq6Sa6_OxA4g7iu-Q",
  "version" : {
    "number" : "6.7.0",
    "build_flavor" : "default",
    "build_type" : "zip",
    "build_hash" : "Unknown",
    "build_date" : "2019-01-24T04:05:16.950403Z",
    "build_snapshot" : true,
    "lucene_version" : "7.6.0",
    "minimum_wire_compatibility_version" : "5.6.0",
    "minimum_index_compatibility_version" : "5.0.0"
  },
  "tagline" : "You Know, for Search"
}

This causes VerifyVersionConstantsIT.testLuceneVersionConstant to fail (log) becuase it tries to pass the version.number through Version.fromString and fromString does not accept -SNAPSHOT qualifiers for versions new than 2.x

elasticsearch/server/src/main/java/org/elasticsearch/Version.java

Lines 297 to 299 in b8be6cb

	if (rawMajor >= 5 && snapshot) { // we don't support snapshot as part of the version here anymore
	throw new IllegalArgumentException("illegal version format - snapshots are only supported until version 2.x");
	}

REPRODUCE WITH:

./gradlew :qa:verify-version-constants:v7.0.0#oldClusterTestRunner -Dtests.seed=D70B4DC789F67CC -Dtests.class=org.elasticsearch.qa.verify_version_constants.VerifyVersionConstantsIT -Dtests.method="testLuceneVersionConstant" -Dtests.security.manager=true -Dtests.locale=es-ES -Dtests.timezone=Antarctica/Rothera -Dtests.distribution=default -Dcompiler.java=11 -Druntime.java=8

It looks we either need to:

1. Drop the qualifier from the main response in 7.0
2. Accept the qualifier in Version.fromString if we're now including them again
3. Work around it in testLuceneVersionConstant (but I suspect that won't be the only place).

[elasticmachine]

Pinging @elastic/es-core-infra

[tvernum]

@atorok I assigned this to you since it stems from your qualifier changes, so I thought you'd be best placed to decide which fix is most appropriate.

[alpar-t]

Thanks @tvernum looks like this is happening on 7.x . We fixed in on master in #38514 but looks like it didn't make it to 7.x.

[alpar-t]

back-ported to both 7.x and 7.0