use hash for nodenum->hostname lookup

[aakash10292]

RDSICDBDBA-1342 describes the issue while migrating from a 16 node cluster to a 24 node cluster. The cause is a overflow resulting in memory corruption.

This patch replaces the static array with a hashmap (dynamically sized). Also adds a test utility bdb trap -> fetch nodenum given a hostname.

Associated plugin branch -> aar_nodenum_lookup