LU-10710 tests: fix run_write_disjoint line continuation

LU-10710 tests: fix run_write_disjoint line continuation

There is a problem with creating a command in
run_write_disjoint() due to a line continuation followed
on the next line by tabs. We need to remove the end
quotation before the line continuation and first
quotation mark on following line.

Test-Parameters: trivial testlist=parallel-scale
Signed-off-by: James Nunez <james.a.nunez@intel.com>
Change-Id: I32dc620dd5c3e3d305d0bf985a096e69c18404d1
Reviewed-on: https://review.whamcloud.com/31645
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Elena Gryaznova <c17455@cray.com>
Reviewed-by: Saurabh Tandan <saurabh.tandan@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>