BSC_Tests: ramdomize IMSI in f_gen_test_hdlr_pars()

Using the same IMSI in each test case makes it harder to correlate
subscriber connections in the SUT with particular test cases.  A
good example is a problem described in OS#5337: some test cases
create dangling subscriber entries that never got released:

  OsmoBSC# show subscriber all
   IMSI             TMSI      Use
   001019876543210  ffffffff  3 (3*paging-start)
   001010000100001  ffffffff  1 (conn)

With this patch I am getting the following output:

  OsmoBSC# show subscriber all
   IMSI             TMSI      Use
   001016017428234  ffffffff  1 (paging-start)
   001014631230680  ffffffff  1 (paging-start)
   001011161500382  ffffffff  1 (paging-start)
   001010000100001  ffffffff  1 (conn)

so I was able to correlate the following test cases:

* (001016017428234) TC_lcs_loc_req_for_active_ms_ta_req,
* (001014631230680) TC_lcs_loc_req_for_active_ms_le_timeout2,
* (001011161500382) TC_cm_service_during_lcs_loc_req,
* (001010000100001) TC_no_msc.

Change-Id: Ie008b5566b207b13cd562c55625bad38c09b3927
Related: OS#5337
1 file changed