tests: 0044interval_overlap_0: Repeat insertion tests with timeout

tests: 0044interval_overlap_0: Repeat insertion tests with timeout

Mike Dillinger reported issues with insertion of entries into sets
supporting intervals that were denied because of false conflicts with
elements that were already expired. Partial failures would occur to,
leading to the generation of new intervals the user didn't specify,
as only the opening or the closing elements wouldn't be inserted.

The reproducer provided by Mike looks like this:

  #!/bin/bash
  nft list set ip filter blacklist4-ip-1m
  for ((i=1;i<=10;i++)); do
        nft add element filter blacklist4-ip-1m {$i.$i.$i.$i}
        sleep 1
  done
  nft list set ip filter blacklist4-ip-1m

which, run in a loop at different intervals, show the different kind
of failures.

Extend the existing test case for overlapping and non-overlapping
intervals to systematically cover sets with a configured timeout.

As reported by Pablo, the test would fail if we keep a one-second
timeout if it runs on a "slow" kernel (e.g. with KASan), using the
libtool wrapper in src/nft as $NFT, because we can't issue 218
commands within one second. To avoid that, introduce an adaptive
timeout based on how many times we can list a single entry with a
fixed one-second timeout.

On a single 2.9GHz AMD Epyc 7351 thread:
                                     test run   nft commands/s  timeout
- src/nft libtool wrapper, KASan:       68.4s          10         32s
- nft binary, KASan:                     5.1s         168          2s
- src/nft libtool wrapper, w/o KASan:   18.3s          37          8s
- nft binary, w/o KASan:                 2.4s         719          1s

While at it, fix expectation for insertion of '15-20 . 50-60' (it's
expected to succeed, given the list), and the reason why I didn't
notice: a simple command preceded by ! won't actually result in
the shell exiting, even if it fails. Add some clearer failure reports
too.

v2:
  - adjust set timeouts to nft commands/s
  - fix checks on expected outcome of insertions and reports

Reported-by: Mike Dillinger <miked@softtalker.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>