MEDIUM: checks: Add matching on log-format string for expect rules

MEDIUM: checks: Add matching on log-format string for expect rules

It is now possible to use log-format string (or hexadecimal string for the
binary version) to match a content in tcp-check based expect rules. For
hexadecimal log-format string, the conversion in binary is performed after the
string evaluation, during health check execution. The pattern keywords to use
are "string-lf" for the log-format string and "binary-lf" for the hexadecimal
log-format string.