LU-9032 tests: syntax error in cleanup_test32_mount

LU-9032 tests: syntax error in cleanup_test32_mount

Fix regular expression in sed parameter.

sed: unmatched '/'

Also make cleanup function common for all test_32*.
Style cleanup.

Signed-off-by: Dmitry Eremin <dmitry.eremin@intel.com>
Change-Id: I6245d0b3c00b0f0f79213263b6c81e9ab6000d11
Reviewed-on: https://review.whamcloud.com/24942
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Faccini Bruno <bruno.faccini@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>