Check for "file not removed" in system test output

Any CI job:

• I:dnssec:file dnssec/ns1/trusted.keys not removed
• I:rpzrecurse:file rpzrecurse/ns3/named.run.prev not removed

system:clang:freebsd11:amd64:

• I:tkey:file tkey/ns1/named.conf-e not removed

system:gcc:sid:amd64:

• I:mirror:file mirror/ns3/_default.nzf not removed

system:gcc:xenial:amd64:

• I:rpzextra:file rpzextra/.cache/v/cache/lastfailed not removed
• I:rpzrecurse:file rpzrecurse/ns3/named.run.prev not removed
• I:shutdown:file shutdown/.cache/v/cache/lastfailed not removed

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Ad 9709e765: Note that print_outstanding_files() of bin/tests/system/run.sh "identified" tsiggss files as "note removed" from the tsig (sic) test on CentOS 8: