TS-2127 Move hostdb.config to var/trafficserver

This eliminates the entire etc/internal directory, and moves the
hostdb.config to the var/trafficserver (depending on configure option
of course). This means hostdb.config and host.db are now in the same
directory, together with all other "state" files:

-rw-r--r-- 1 nobody nobody        71 Aug 16 09:51 hostdb.config
-rw-r--r-- 1 nobody nobody 268435456 Aug 16 09:52 cache.db
-rw-r--r-- 1 root   root           6 Aug 16 10:47 cop.lock
-rw-r--r-- 1 nobody nobody         6 Aug 16 10:47 manager.lock
srwxr-xr-x 1 nobody nobody         0 Aug 16 10:47 process_server
srwxr-xr-x 1 nobody nobody         0 Aug 16 10:47 mgmtapisocket
srwxr-xr-x 1 nobody nobody         0 Aug 16 10:47 eventapisocket
-rw-r--r-- 1 nobody nobody         6 Aug 16 10:47 server.lock
-rw-r--r-- 1 nobody nobody      1068 Aug 16 10:50 stats.snap
-rw-r--r-- 1 nobody nobody  25935872 Aug 16 10:50 host.db
-rw------- 1 nobody nobody     64208 Aug 16 10:50 records.snap