[SPARK-1150] fix repo location in create script

https://spark-project.atlassian.net/browse/SPARK-1150

fix the repo location in create_release script

Author: Mark Grover <mark@apache.org>

Closes #48 from CodingCat/script_fixes and squashes the following commits:

01f4bf7 [Mark Grover] Fixing some nitpicks
d2244d4 [Mark Grover] SPARK-676: Abbreviation in SPARK_MEM but not in SPARK_WORKER_MEMORY
Switching to in-memory-shuffle based on changes described in https://github.com/amplab/graphx/commits/sigmod-memory-shuffle