cosmetic: log IMSI='<imsi>', log "no such subscriber"

In LOGHLR and LOGAUC, log IMSI='<imsi>' instead of just <imsi>:
In the log, it is not always obvious to the reader that the printed number
refers to an IMSI (vs. an MSISDN or in the future an IMEI).

In db_get_auth_data(), log "No such subscriber" instead of just "Unknown", to
clarify what exactly is meant.

Change-Id: I2ec8ab5e67d4e95083f6e39232fc91ebaa080cb8
2 files changed