Clean up ovsec_kadmd.c

Clean up ovsec_kadmd.c

Fix code formatting issues.  Use static scope when possible, and put
all helper functions before main so that forward declarations aren't
needed.  Use GSS_KRB5_NT_PRINCIPAL_NAME instead of constructing it
with gss_str_to_oid, and get rid of display_status as that was the
only use.  Replace large verbose function comments with concise ones.
Factor out main loop setup and KDB keytab setup into helper functions.
Create a helper function fail_to_start for logging and exiting on
initialization failures, and use it instead of the large cleanup
blocks in main.

Some initialization error messages have changed; no other functional
changes.