[stats] better scuba and log output for longest_proc_duration_heap
[stats] better scuba and log output for longest_proc_duration_heap

Summary:
The scuba fields had the proc name inside them, which makes their
usefulness limited as they are different keys every time. Instead, key
the results on the rank and do not emit proc names to scuba.

Prettier formatting: Sample before:
```
[1409609][      debug]   longest_proc_duration_heap= [engine_aep -> 17174ms, aep_mod_exp_dh -> 16562ms, aep_mod_exp -> 16399ms, BN_mod_exp -> 15711ms, des_ede_cfb64_cipher -> 13102ms, DES_ede3_cfb64_encrypt -> 96
41ms, BN_mod_exp_mont_word -> 7513ms, bind_aep -> 7507ms, ENGINE_new -> 7321ms, DES_encrypt3 -> 6935ms]
```

Sample after:
```
[1471107][      debug]   longest_proc_duration_heap= [
[1471107][      debug]      16ms: no_early_return_manifest_bad_FN
[1471107][      debug]      10ms: crash_deref_ptr
[1471107][      debug]       6ms: no_early_return_bad_latent_FN
[1471107][      debug]       6ms: return_internally_aliased_pointer
[1471107][      debug]       4ms: deref_null_from_aliased_history
[1471107][      debug]       2ms: deref_ptr
[1471107][      debug]   ]
```

Reviewed By: ngorogiannis

Differential Revision: D41520647

fbshipit-source-id: 277cf75397e1eeaf27e27366d24072bc4ccdfb79

facebook/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer