ftests: cleanup return statements

ftests: cleanup return statements

This patch cleans up a few oddities around return statements:
1. Removes redundant return statements across the ftests/*, mostly in
   the function prereqs and a few other places too.
2. Follows the same function template for prereqs, across the ftests/*.,
   and removes the checks for success on return from prereqs function,
   those will be true always.
3. Also, replace consts.TEST_PASSED, None with pass for functions, that
   serves as stub and remove the return value checks for stubs.

Signed-off-by: Kamalesh Babulal <kamalesh.babulal@oracle.com>
Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com>
(cherry picked from commit 0c65a402990d8657637b10bb4ae02f99ae575082)