lancelot: detect and handle Jenkins CI environment

lancelot: detect and handle Jenkins CI environment

Make the test behave in Jenkins similarly as it behaves in Pulse:

  - a test run in Jenkins is not an ad-hoc run

  - the JENKINS_HOME environment variable implies we are running in
    Jenkins

  - the GIT_BRANCH environment variable, set by the Jenkins git plugin,
    is equivalent to PULSE_GIT_BRANCH

  - there is no equivalent to PULSE_TESTR_BRANCH, since testr is no
    longer used

Change-Id: I89ffeec659b4adaab309d8b93ad793ce640029c7
Reviewed-by: aavit <qt_aavit@ovi.com>