[SPARK-3788] [yarn] Fix compareFs to do the right thing for HDFS namespaces (1.1 version).

HA and viewfs use namespaces instead of host names, so you can't
resolve them since that will fail. So be smarter to avoid doing
unnecessary work.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #2650 from vanzin/SPARK-3788-1.1 and squashes the following commits:

174bf71 [Marcelo Vanzin] Update comment.
0e36be7 [Marcelo Vanzin] Use Objects.equal() instead of ==.
772aead [Marcelo Vanzin] [SPARK-3788] [yarn] Fix compareFs to do the right thing for HA, federation (1.1 version).