Allow to keep deleted files also in non-HSM archival OSDs

This is now controlled by a new flag-bit OSDDB_DONT_UNLINK in the
OSDDB entry. Another new flag-bit OSDDB_WITH_HSM_PATH is required
for HPSS-OSDs when the same server has other archival OSDs. The last one can be set only by "osd setosd" the other one also during "osd createosd".
There were some bugs with init_osddb_client which I solved by using
local my_init_osddb_client routines in rxosd.c and osd.c. the rxosd did not
fill the cell name into the osdid-file in the partition which prevented
"afsd -check-osd" to work correctly and osd did not use the user's token,
so only commands which can be run unauthenticated were possible.
For backward compatibility with older versions of the osddb the
OSDDB_WITH_HSM_PATH ("setosd -hpss 1") is only required when another archival
OSD is present.