HDDS-5442. Datanode HTTP server fails to start in ozonesecure due to wrong keytab name

[adoroszlai]

What changes were proposed in this pull request?

Fix filename of datanode HTTP keytab in ozonesecure env, which caused:

[main] ERROR ozone.HddsDatanodeService: HttpServer failed to start.
...
Caused by: javax.servlet.ServletException: Keytab does not exist: /etc/security/keytabs/datanode.keytab

https://issues.apache.org/jira/browse/HDDS-5442

How was this patch tested?

Started ozonesecure cluster, no error related to HTTP server:

[main] INFO http.BaseHttpServer: Starting Web-server for hddsDatanode at: http://0.0.0.0:9882
[main] INFO http.BaseHttpServer: Hadoop Security Enabled: true Ozone Security Enabled: true Ozone HTTP Security Enabled: true 
[main] INFO http.BaseHttpServer: HttpAuthType: hdds.datanode.http.auth.type = kerberos
...
[main] INFO http.BaseHttpServer: HTTP server of hddsDatanode listening at http://0.0.0.0:9882

Regular CI:
https://github.com/adoroszlai/hadoop-ozone/actions/runs/1031181668

[mukul1987]

LGTM

[xiaoyuyao]

LGTM, +1.

[adoroszlai]

Thanks @mukul1987 for the review and @xiaoyuyao for merging this.