dynamic_cert_mem_cache_size option related fixes

dynamic_cert_mem_cache_size option related fixes

This patch fixes the following problems:

1) The dynamic_cert_mem_cache_size does not change on reconfigure

2) When dynamic_cert_mem_cache_size of http_port set to 0 then:

   a) The dynamic certs cache is grow unlimited.
      This patch just disables certificates caching when this option set to 0.

   b) Huge amount of memory appeared as free cache memory in  "Cached ssl
      certificates statistic" page of cache manager.
      This problem caused because of a signed to unsigned int conversion.

This is a Measurement Factory project