To ensure Perl invocations within tests call the same Perl binary used
for running the tests, as specified or auto-detected via `PERL` env
(autotools) or `PERL_EXECUTABLE` setting (cmake). Instead of the first
`perl` executable found in `PATH`.)
Cherry-picked from #14949Closes#15097
Also introduce 'notexists' for verifying that directory entries do not
exist after a test. Now an explicit supported feature instead of using
"funny" perl in postcheck.
Closes#15046
The threee tags `<name>`, `</name>` and `<command>` were frequently used
with a leading space that this removes. The reason this habbit is so
widespread in testcases is probably that they have been copy and pasted.
Hence, fixing them all now might curb this practice from now on.
Closes#12028
These files are generated by the test servers and must therefore be
found in the log directory to make them available to only those servers
once multiple test runners are executing in parallel. They must also not
be deleted with the log files, so they are stored in the pidfile
directory.
Ref: #10818Closes#10875
