MEDIUM: checks: Implement redis check using tcp-check rules

MEDIUM: checks: Implement redis check using tcp-check rules

A share tcp-check ruleset is now created to support redis checks. This way no
extra memory is used if several backends use a redis check.

The following sequence is used :

  tcp-check send "*1\r\n$4\r\nPING\r\n"

  tcp-check expect string "+PONG\r\n" error-status "L7STS" \
      on-error "%[check.payload(),cut_crlf]" on-success "Redis server is ok"