LU-17047 tests: sanity/77c ensure ost debug_path is valid

LU-17047 tests: sanity/77c ensure ost debug_path is valid

test_77c has been failing intermittently for a while due
to either debug_param not being set properly before this test is
invoked or due to silent failure of getting the param from the
remote node.

Try to avoid these spurios test flakiness by forcing the debug_path
parameter to the expected setting during test startup.
A test shouldn't depend on no residuals being present from unrelated
prior tests anyway.

If need be we can add a dedicated test that only verifies that we
can set debug_path to a specific value and then read the value back.

Test-Parameters: trivial testgroup=rolling-upgrade-client1
Test-Parameters: testgroup=rolling-downgrade-mds
Test-Parameters: testgroup=rolling-downgrade-client2
Test-Parameters: testgroup=rolling-upgrade-client2
Signed-off-by: Ronnie Sahlberg <rsahlberg@whamcloud.com>
Change-Id: I4aae3e422d8f492a7877fbe20a6c553afc35e998
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/56643
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>