Create a Karaf post-install script for tests

Create a Karaf post-install script for tests

- add a post-install shell script for Karaf and tests purpose
  This post-install script will be copied at build-time from
  src/main/assembly/ressources to target/assembly/ressources
- move the tox.ini sed command used to patch Karaf exec into this script
- update this command since there is no more quoting hell issues
- update tox.ini accordingly

JIRA: TRNSPRTPCE-482
Signed-off-by: guillaume.lambert <guillaume.lambert@orange.com>
Change-Id: Iac1bfa3b4bf7a8d0e55130abf2f4cbf349f14ba4