Update etl scripts

Contains environments variables for etl scripts. Factorize some code and creates
symbolic links for hraven-core.jar and hraven-etl.jar if needed. Etl scripts now source this file.

Source hraven-etl-env.sh and add default values for costFile and rawFileSizeLimit.
Also calls jobFilePreProcessor.sh and jobFileProcessor.sh  with right arity and parameters from now.

source hraven-etl-env.sh

source hraven-etl-env.sh and add defaultRawFileSizeLimit to parameters

exports HBASE_CLASSPATH
Now set a default value for hadoop property mapreduce.map.memory.mb
which is not set in yarn conf by default
update etl scripts + memorymb default value

hraven-etl-env.sh now detects last version of hraven-core and hraven-etl
before linking to it.

Constants.java : defautl value for map memory mb set up

JobHistoryFileParserHadoop2.java : now set default value for memory mb using Constants.java
Update Constants and JobHistoryFileParserHadoop2

Constants.java
Now set hadoop default values for MAP_MEMORY_MB and REDUCE_MEMORY_MB

JobHistoryFileParser2.java
Now cheks if required key is mapreduce.map.memory.mb or mapreduce.reduce.memory.mb
and gets appropriate default value from Constants.java in case the config doesnt contain
the needed property.
Update JobHistoryFileParserHadoop2.java

Replaced "mapreduce.map.memory.mb" by Constant.java value
Replaced "mapreduce.reduce.memory.mb" by Constant.java value
Updated memorymb to avoid NPE
Merge pull request #88 from criteo/master

Update etl scripts and memorymb default value
Issue #92 Refactor code in TaskDetails
Merge pull request #93 from vrushalic/AM_finish_time

Issue #92 Refactor code in TaskDetails
implement /tasks REST endpoint
correct log message for /tasks endpoint
new addTasks(List<TaskDetails>) method to JobDetails
pull put logic to download url data in rest client
add ability to hydrate a Flow with task details to rest client
add jackson annotations to task-related classes
add timer to /tasks rest endpoint
remove the hydrate function from REST client
add timing logging to /tasks endpoint
add toString to all keys and standardize their construction
pull out UrlDataLoader to its own class