Add details when BlockManager heartbeats time out

Makes it more clear what the threshold was for tuning spark.storage.blockManagerSlaveTimeoutMs

Before:
WARN  "Removing BlockManager BlockManagerId(201304022120-1976232532-5050-27464-0, myhostname, 51337) with no recent heart beats

After:
WARN  "Removing BlockManager BlockManagerId(201304022120-1976232532-5050-27464-0, myhostname, 51337) with no recent heart beats: 19216ms exceeds 15000ms
Fix tests from different projects running in parallel in SBT 0.12
Merge branch 'master' of github.com:mesos/spark
Merge pull request #561 from ash211/patch-4

Add details when BlockManager heartbeats time out
Merge branch 'master' of https://github.com/mesos/spark into master-2.10
Fixed missing '+'