When first parameter is check_only, the tcpflood funtion shall not
abort the test itself (The fail is intended if this option is set).
closes issue #3625
This leads to a refactoring of the looking code; issue was caused
by new TTL cache expiration code which placed not semantics on the
cache. These were not properly handled under all circumstances.
Also added a test based on imtcp-tls-ossl-basic.sh which tests
the new -k parameter with tcpflood called:
imtcp-tls-ossl-basic-tlscommands.sh
Fixed OpenSSL error reporting in tcpflood which was running into
a loop when OpenSSL error stack was printed out.
