travis.yml: replace test-capability with a script exiting with 77

travis.yml: replace test-capability with a script exiting with 77

The test is currently failing when run under ASan in a docker container:
```
--- command ---
SYSTEMD_KBD_MODEL_MAP='/build/src/locale/kbd-model-map' PATH='/build/build:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin' SYSTEMD_LANGUAGE_FALLBACK_MAP='/build/src/locale/language-fallback-map' /build/build/test-capability
--- stderr ---
have ambient caps: yes
Capabilities:= cap_chown,cap_dac_override,cap_dac_read_search,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_linux_immutable,cap_net_bind_service,cap_net_broadcast,cap_net_admin,cap_net_raw,cap_ipc_lock,cap_ipc_owner,cap_sys_module,cap_sys_rawio,cap_sys_chroot,cap_sys_ptrace,cap_sys_pacct,cap_sys_admin,cap_sys_boot,cap_sys_nice,cap_sys_resource,cap_sys_time,cap_sys_tty_config,cap_mknod,cap_lease,cap_audit_write,cap_audit_control,cap_setfcap,cap_mac_override,cap_mac_admin,cap_syslog,cap_wake_alarm,cap_block_suspend,cap_audit_read+eip
Capabilities:= cap_dac_override,cap_net_raw+ep
==7021==LeakSanitizer has encountered a fatal error.
==7021==HINT: For debugging, try setting environment variable LSAN_OPTIONS=verbosity=1:log_threads=1
==7021==HINT: LeakSanitizer does not work under ptrace (strace, gdb, etc)
Assertion 'WIFEXITED(status) && WEXITSTATUS(status) == 0' failed at ../src/test/test-capability.c:71, function fork_test(). Aborting.
-------
```

https://api.travis-ci.org/v3/job/452349948/log.txt