server: Serve well-known bus names
server: Serve well-known bus names

Prior to this patch the mapper served unique connection
names.  Serve well-known names instead so clients can
cache mapper lookup results.

Tested: Manually verified mapper content and signals in the
  following workflows:
   - Service discovery
   - Interface added post discovery
   - Interface removed post discovery
   - Bus disconnect post discovery
   - Bus connect post discovery
   - Association added post discovery
   - Association removed post discovery
   - Association modified post discovery
Signed-off-by: Brad Bishop <713d098c0be4c8fd2bf36a94cd08699466677ecd@fuzziesquirrel.com>
Change-Id: Ia697c86dc287b6e289ea6d84364b24ef9a2c18c8

openbmc/phosphor-objmgr,openbmc/phosphor-objmgr