webadmin: Small cleanup in RestApiSessionManager

Acquiry of new session vs. keep-alive of existing session
logical scenarios represented by two separate methods.

REST CSRF token request header represented by a separate
String constant to avoid confusion with JSESSIONID header
containing actual REST session ID on HTTP response.

Change-Id: I98ad53785726c4ed1a8b1eaaf4fd473052496c3e
Signed-off-by: Vojtech Szocs <vszocs@redhat.com>
build: Add explicit execution ID for maven-jar-plugin:test-jar

By default, maven-jar-plugin:test-jar is executed when building
all child projects, resulting in "test JAR" file like following:

  target/${artifactId}-${version}-tests.jar

This patch adds execution ID for maven-jar-plugin:test-jar so
that some child projects may decide to skip creation of above
mentioned "test JAR" file.

As a side note, explicit execution IDs are always better than
relying on Maven-generated (implicit) execution IDs.

Change-Id: I1f22b179436f29ca8022f33607c10af6c6f2a9ef
Signed-off-by: Vojtech Szocs <vszocs@redhat.com>