Bug 4843 pt1: ext_edirectory_userip_acl refactoring for GCC-8 (#204)

Bug 4843 pt1: ext_edirectory_userip_acl refactoring for GCC-8 (#204)

Proposed changes to this helper to fix strcat / strncat buffer
overread / overflow issues.

The approach takes three parts:

* adds a makeHexString function to replace many for-loops
  catenating bits of strings together with hex conversion into a
  second buffer. Replacing with a snprintf() and buffer overflow
  handling.

* a copy of Ip::Address::lookupHostIp to convert the input
  string into IP address binary format, then generate the hex
  string using the above new hex function instead of looped
  sub-string concatenations across several buffers.
  This removes all the "00" and "0000" strncat() calls and
  allows far simpler code even with added buffer overflow
  handling.

* replace multiple string part concatenations with a few simpler
  calls to snprintf() for all the search_ip buffer constructions.
  Adding buffer overflow handling as needed for the new calls.