Fix warnings reported by static analysis.

- ensure that strings are \0 terminated (most of this is already
handled on higher level anyway)

- fix resource leak in error path in tcrypt.c

- fix time of check/time of use race in sysfs path processing

- insruct Coverity scanner to ignore constant expression in random.c
(it is intented to stop compile-time misconfiguration of RNG that would be fatal)

lib/random.c

@@ -234,9 +234,11 @@ void crypt_random_exit(void)
 
 int crypt_random_default_key_rng(void)
 {
+	/* coverity[pointless_string_compare] */
 	if (!strcmp(DEFAULT_RNG, RANDOM_DEVICE))
 		return CRYPT_RNG_RANDOM;
 
+	/* coverity[pointless_string_compare] */
 	if (!strcmp(DEFAULT_RNG, URANDOM_DEVICE))
 		return CRYPT_RNG_URANDOM;