LU-13116 tests: properly clean keyring in sanity-sec test_30

LU-13116 tests: properly clean keyring in sanity-sec test_30

sanity-sec test_30 makes use of a bogus key to test Lustre behaviour
in case of invalid shared key. This bogus key must be cleaned and
removed properly so that it does not interfere with subsequent tests.

Test-Parameters: trivial envdefinitions=SHARED_KEY=true testlist=sanity-sec
Test-Parameters: envdefinitions=SHARED_KEY=true testlist=sanity-sec
Test-Parameters: envdefinitions=SHARED_KEY=true testlist=sanity-sec
Test-Parameters: envdefinitions=SHARED_KEY=true testlist=sanity-sec
Test-Parameters: envdefinitions=SHARED_KEY=true testlist=sanity-sec
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I32d6b70948b2fedfb60f2750f56ef772a404d08c
Reviewed-on: https://review.whamcloud.com/37151
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>