test/nvmf: reduce connect_disconnect iterations

Reduce connect-disconnect iterations to 5 to
save execution time. 5 should be enough for a
basic test which is significantly extended in
nightly version.

Change-Id: I44549ccb96f69e925471acc91a1704a0b9e61d2b
Signed-off-by: Karol Latecki <karol.latecki@intel.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/16212


Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: John Kariuki <John.K.Kariuki@intel.com>
Reviewed-by: Shuhei Matsumoto <smatsumoto@nvidia.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>