[keycloak-dev] Added KEYCLOAK_DEV_PORT env for KeycloakSever

KeycloakServer now checks KEYCLOAK_DEV_PORT environment variable. If it's set that'll be used as the port to start the server on. As I prefer to have KeycloakServer running on 8080 I've set this env variable in my profile. Note: this doesn't affect running the testsuite (still runs on port 8081) or when Keycloak is deployed to WildFly/EAP