replace file placement to consistent hash

Signed-off-by: Elena V <elena.viter@yahoo.com>
impala -> impala-to-go. hdfs dependencies removed. Impala interation with dfs becomes generic.
Explicit hdfs integration is removed from Impala. Added cache layer (in progress).
Pass staging changes
move boost thirdparty multiprecision pre-c++11 definitions from runtime to common. intorduce tests for dfs_cache
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Implement Estimate and Prepare commands requests infrastructure and flow. Add requests local management. Define active queue and history of requests. Add shutdown support to cache manager.
Merge branch 'libdfscache' of https://github.com/ImpalaToGo/ImpalaToGo into libdfscache

Readme was added
Assign raii behavior to namenode's dfs connection so that the connection is reset to free-to-use once the dfs adaptor borrowing the connection completes its task. Made via a scoped-living wrapper on the dfs connection
make cache requests history light-weight but descriptive enough to represent the request. In the same way as active requests, it is accessible in O(1). Separate sync requests queue.
provide shutdown-like finalization in the cache manager
CacheMgr - add handling of non-success client request insertion. Add unit tests for Cache Manager Requests handling API.
Add hadoop file system adaptive layer. Map required hadoop types to c++ types.
Extend Hadoop FileSystem adaptive layer with org.apache.hadoop.fs.FSDataInputStream and org.apache.hadoop.fs.FSDataOutputStream APIs
Add Hadoop libhdfs jni-helper and its dependencies to work with jni on hadoop types