Yum versionlock does not properly lock elasticsearch-oss

[conet]

Elasticsearch version
6.3.2

Role version: (If using master please specify github sha)
4ec1f3b

JVM version (java -version):
openjdk version "1.8.0_181"
OpenJDK Runtime Environment (build 1.8.0_181-b13)
OpenJDK 64-Bit Server VM (build 25.181-b13, mixed mode)

OS version (uname -a if on a Unix-like system):

Description of the problem including expected versus actual behaviour:

Yum versionlock does not properly lock elasticsearch-oss when es_enable_xpack is false, instead it always locks elasticsearch see this https://github.com/elastic/ansible-elasticsearch/blob/master/tasks/elasticsearch-RedHat-version-lock.yml#L7

Playbook:

    es_version: "6.3.2"
    es_version_lock: true
    es_enable_xpack: false

[Crazybus]

@conet nice catch! I just opened a PR to fix this up.