[GIRAPH-1089] Fix a bug in out-of-core infrastructure

Summary: This diff fixes a bug in out-of-core infrastructure that caused user requirement (max number of partitions in memory) for fixed out-of-core strategy get violated. The cause of the problems was the un-clear definition of in-memory partitions. In this diff, we distinguish the partitions that are entirely in memory from those that are partially in memory.

Test Plan:
mvn clean verify

Reviewers: dionysis.logothetis, sergey.edunov, maja.kabiljo

Reviewed By: maja.kabiljo

Differential Revision: https://reviews.facebook.net/D60573
8 files changed