Swarm statistic report failed if there are no bugs

[Andrey Sledzinskiy]

Steps:
1. Clone fuel-qa repo and cd to fuel-qa
2. export TESTRAIL_TEST_SUITE='Upgrade Centos Cluster'
3. export USE_CENTOS=true
4. export USE_UBUNTU=false
5. python fuelweb_test/testrail/report.py -v -l -j 8.0.swarm.runner -s

2015-11-26 21:23:30,169 - INFO - No linked to test cases bugs found
Traceback (most recent call last):
  File "fuelweb_test/testrail/report.py", line 698, in <module>
    main()
  File "fuelweb_test/testrail/report.py", line 695, in main
    bug_results)
TypeError: coercing to Unicode: need string or buffer, NoneType found

We need to return empty string in case no bugs are present

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/250721

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/250721
Committed: https://git.openstack.org/cgit/openstack/fuel-qa/commit/?id=b422dcc3c93fe850274164384f759f82105d8583
Submitter: Jenkins
Branch: master

commit b422dcc3c93fe850274164384f759f82105d8583
Author: asledzinskiy <email address hidden>
Date: Fri Nov 27 12:00:21 2015 +0200

    Fix swarm statistic reporter

    - In case we don't have linked bugs in suite
    we need to return empty string

    Change-Id: I5ca2adf3450e82ccb4784b3eebd8f62e7a44f2f8
    Closes-Bug: #1520503

[Fuel Devops McRobotson (fuel-devops-robot)]

Related fix proposed to branch: master
Change author: Artem Panchenko <email address hidden>
Review: https://review.fuel-infra.org/14252

[Fuel Devops McRobotson (fuel-devops-robot)]

Reviewed: https://review.fuel-infra.org/14252
Submitter: Aleksandra Fedorova <email address hidden>
Branch: master

Commit: 0482670a3f84f717c62a66a589afb03765cc6e60
Author: Artem Panchenko <email address hidden>
Date: Mon Nov 30 09:43:01 2015

Remove legacy part from reporter job

Since we don't run upgrade tests anymore, remove
legacy code from reporter job.

Change-Id: I603f31599136ef12f2d8668a3304329ac0345861
Related-bug: #1520503