Minor logging fixes

[msimberg]

This fixes some minor issues with the logging output related to hostnames and ranks:

• The hostname was printed twice in multi-rank runs.
• The thread and pool indices were printed as hexadecimal which in my opinion doesn't make much sense; they're now printed as decimal.
• The MPI rank is retrieved with MPI_Comm_rank first, if MPI is initialized.
• If the MPI rank can't be retrieved with MPI_Comm_rank, the way environment variables are checked is slightly changed to prioritize environment variable names that are more likely to contain the rank.

[pika-bot]

Performance test report

pika Performance

Comparison

BENCHMARK	RESULT
Task Overhead - Create Thread Hierarchical - Latch	-

Info

Property	Before	After
pika Commit	0abc084	4192aff
pika Datetime	2024-02-19T15:15:15+00:00	2024-05-27T09:12:34+00:00
Compiler	/apps/daint/SSL/pika/spack/lib/spack/env/clang/clang++ 11.0.1	/apps/daint/SSL/pika/spack/lib/spack/env/clang/clang++ 11.0.1
Hostname	nid00025	nid01209
Datetime	2024-02-19T16:26:16.072067+01:00	2024-05-27T11:23:01.786541+02:00
Clustername	daint	daint
Envfile

Explanation of Symbols

Symbol	MEANING
=	No performance change (confidence interval within ±1%)
(=)	Probably no performance change (confidence interval within ±2%)
(+)/(-)	Very small performance improvement/degradation (≤1%)
+/-	Small performance improvement/degradation (>10%)
++/--	Large performance improvement/degradation (>10%)
+++/---	Very large performance improvement/degradation (>10%)
?	Probably no change, but quite large uncertainty (confidence interval with ±5%)
??	Unclear result, very large uncertainty (±10%)
???	Something unexpected…

[aurianer]

LGTM thanks!