Test: memory leak in single onion service test

Found by the expensive hardening:

hs/single_onion_poisoning_create_dir_none: [forking] 
=================================================================
==29309==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 102 byte(s) in 2 object(s) allocated from:
    #0 0x7f93a6775eb0 in __interceptor_malloc (/usr/lib/x86_64-linux-gnu/libasan.so.3+0xc6eb0)
    #1 0x7f93a41dcbf9 in __strdup (/lib/x86_64-linux-gnu/libc.so.6+0x8cbf9)

SUMMARY: AddressSanitizer: 102 byte(s) leaked in 2 allocation(s).
OK
hs/single_onion_poisoning_create_dir1: [forking] 
=================================================================
==29311==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 102 byte(s) in 2 object(s) allocated from:
    #0 0x7f93a6775eb0 in __interceptor_malloc (/usr/lib/x86_64-linux-gnu/libasan.so.3+0xc6eb0)
    #1 0x7f93a41dcbf9 in __strdup (/lib/x86_64-linux-gnu/libc.so.6+0x8cbf9)

SUMMARY: AddressSanitizer: 102 byte(s) leaked in 2 allocation(s).
OK
hs/single_onion_poisoning_create_dir2: [forking] 
=================================================================
==29313==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 102 byte(s) in 2 object(s) allocated from:
    #0 0x7f93a6775eb0 in __interceptor_malloc (/usr/lib/x86_64-linux-gnu/libasan.so.3+0xc6eb0)
    #1 0x7f93a41dcbf9 in __strdup (/lib/x86_64-linux-gnu/libc.so.6+0x8cbf9)

SUMMARY: AddressSanitizer: 102 byte(s) leaked in 2 allocation(s).
OK
hs/single_onion_poisoning_create_dir_both: [forking] 
=================================================================
==29315==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 102 byte(s) in 2 object(s) allocated from:
    #0 0x7f93a6775eb0 in __interceptor_malloc (/usr/lib/x86_64-linux-gnu/libasan.so.3+0xc6eb0)
    #1 0x7f93a41dcbf9 in __strdup (/lib/x86_64-linux-gnu/libc.so.6+0x8cbf9)

SUMMARY: AddressSanitizer: 102 byte(s) leaked in 2 allocation(s).
OK

Patch coming up.