LU-1030 test: delete test file at the end of test script

LU-1030 test: delete test file at the end of test script

At sanity.sh:test_49, we need to delete the test file after test is
finished otherwise the following test cases may fail due to lack of
storage capacity.

Signed-off-by: Jinshan Xiong <jinshan.xiong@whamcloud.com>
Change-Id: Iec9e93f1a4844156345608bf9f7a9bf679b36253
Reviewed-on: http://review.whamcloud.com/3158
Reviewed-by: Yu Jian <yujian@whamcloud.com>
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>