[client] replace Equals() with operator==()

This patch replaces the 'bool Equals(const X&)' method for Partition and
PartitionSchema classes with 'bool operator==(const X&)'.

For KuduSchema and KuduColumnSchema, both operator==() and operator!=()
were introduced, and the Equals() method was marked as deprecated since
KuduSchema's and KuduColumnsSchema's API are public at this point.

I decided to perform minor refactoring while changing other code around:
the presence of Equals() method looks a bit lame in a C++ API.

This patch doesn't contain any functional modifications.

Change-Id: I4a95534835c93b1fb7a3ca1f311c530572c50ad2
Reviewed-on: http://gerrit.cloudera.org:8080/17558
Tested-by: Kudu Jenkins
Reviewed-by: Andrew Wong <awong@cloudera.com>
11 files changed