Fix testcases to call tst_exit() on exit

Fix all testcases that does not propagate test result from the main().

This patch was created with following coccinelle sematic patch:

@@ expression E;@@
setup()
...
- return E;
+ tst_exit();

(which basically says to replace all return statements that follow call
 to setup() with tst_exit())

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
Comments cleanup.

Cleanup testcases changed by previous commit.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
Remove useless malloc() casts.

Created with coccinelle patch:

@@
expression E1, E2;
type T;
@@
- E1 = (T)malloc(E2)
+ E1 = malloc(E2)

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
Remove all useless NULL casts.

Created with coccinelle patch:

@@
type T;
@@
-(T) NULL
+ NULL

Hint:
You have to disable isomorphisms by pointing --iso-file to empty file

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>