Fixed compiler warning about rule of three violation

Added explicit copy assignment operator to BlockSetInfoType.
While at it, eliminated a couple of uses of the copy assignment
operator where .clear() could be used instead.

Change-Id: I8426d184c21f1cc938bf2c5856557c0b2f8ebc50
Merge topic 'rule-of-3-exodus' into master

a76e204c Fixed compiler warning about rule of three violation