test-hostname-pick-word: add a simple test to check word selection

This is useful to check if how fast the code is (painfully slow) and whether
worlds indeed are selected with a flat distribution probability (they are).

The code is slow because the hashing and because chaseat is exteremely
inefficient :(

src/shared/hostname-setup.c

@@ -369,7 +369,7 @@ static int pick_word_linear_scan(FILE *f, off_t offset, char **ret) {
         }
 }
 
-static int hostname_pick_word(sd_id128_t mid, size_t pos, char **ret) {
+int hostname_pick_word(sd_id128_t mid, size_t pos, char **ret) {
         static const sd_id128_t word_key = SD_ID128_MAKE(2d,9f,1c,7a,4b,8e,43,11,9a,6d,5f,02,c8,77,e3,14);
         _cleanup_fclose_ FILE *f = NULL;
         struct stat st;

src/shared/hostname-setup.h

@@ -22,6 +22,7 @@ int read_etc_hostname(const char *path, bool substitute_wildcards, char **ret);
 void hostname_update_source_hint(const char *hostname, HostnameSource source);
 int hostname_setup(bool really);
 
+int hostname_pick_word(sd_id128_t mid, size_t pos, char **ret);
 int hostname_substitute_wildcards(const char *name, char **ret);
 
 char* get_default_hostname(void);