LU-8021 tests: Add leading $ to "DEBUGSAVE_SERVER"

LU-8021 tests: Add leading $ to "DEBUGSAVE_SERVER"

Add leading $ to "DEBUGSAVE_SERVER", otherwise the check is always
true and the code tries to restore an empty string and it produces
a lot of spurious error messages in the test logs.

Test-Parameters: trivial
Signed-off-by: Emoly Liu <emoly.liu@intel.com>
Change-Id: I4e9206bc312af22fea22bf6ab634469439008003
Reviewed-on: http://review.whamcloud.com/22586
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Reviewed-by: Parinay Kondekar <parinay.kondekar@seagate.com>