LU-8659 tests: use runcon in sanity-selinux

LU-8659 tests: use runcon in sanity-selinux

In order to switch to other SELinux context, use runcon
instead of 'ssh user@localhost'.
This requires the SELinux policy to allow transitions from
unconfined_t to user_t and guest_t:
allow unconfined_r guest_r;
allow unconfined_r user_r;

Test-Parameters: trivial clientselinux testlist=sanity-selinux
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I8f45dfe71d95d03af0c3577f46c91b47232d958a
Reviewed-on: https://review.whamcloud.com/23962
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Saurabh Tandan <saurabh.tandan@intel.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>