Allow tox tests with Karaf to run in parallel

Allow tox tests with Karaf to run in parallel

- rework tox depends parameter to allow 2 instances of Karaf to be run
  in parallel
- modify buildcontroller process to add specific Karaf build folders
  for each test suite. Karaf instances are tighly coupled to their build
  folder. Using a separate log file is not enough to allow concurrent
  accesses to work properly.
- create an environment variable and adapt tests script accordingly

JIRA: TRNSPRTPCE-482
Signed-off-by: Guillaume Lambert <guillaume.lambert@orange.com>
Change-Id: I7fb608546beaaa19f0b046809c451303bd64c097