Added Random test for ShardAllocator.

This test will make random allocation decision on a growing and
shrinking cluster leading to a random distribution of the shards.
After a certain amount of iterations the test allows allocation unless
the same shard is already allocated on a node and balances the cluster
to gain optimal balance.
Added total, successful shard info to search related asserts in ElasticsearchAssertions

Rewrote SimpleSearchTests assertion to use that.
Add more trace logging if shard allocation is throttled
Changed expectedOperationsPerItem from AtomicInteger array to AtomicReferenceArray<AtomicInteger>.
Made node stopping / starting less aggressive in RecoveryPercolatorTests.
SearchWhileCreatingIndexTests didn't always supply enough node for write consistency requirements and thus hanged.

Added more debug logging to TransportShardReplicationOperationAction

*Changed* node naming in tests from GUIDs to node# based naming as they are much easier to read
Allow up to 10% unbalance in random allocator tests
Added IDs to the community clients docs, to control HTML page names
Used ElasticsearchAssertions to check count result in RecoveryWhileUnderLoadTests
Fixed close index when the index is already closed

Closes #3601
Added log lines to log (debug level) acknowledgements regarding index alias creation and index state change
Added new iteration to RecoveryWhileUnderLoadTests

We want to check whether the issue causing the test to fail would be fixed by an additional refresh or not
Search action now log in debug what shards/nodes were used before moving to second phase
Added  a debug log for executing a refresh request on a shard.
Previously added logging in TransportRefreshAction caused NPE if search shards had errors (or was not yet started/assigned)
Better formatting for logging in TransportRefreshAction
Restructured the transport action code for multi percolate api.
Add 'min_input_len' to completion suggester

Restrict the size of the input length to a reasonable size otherwise very
long strings can cause StackOverflowExceptions deep down in lucene land.
Yet, this is simply a saftly limit set to `50` UTF-16 codepoints by default.
This limit is only present at index time and not at query time. If prefix
completions > 50 UTF-16 codepoints are expected / desired this limit should be raised.
Critical string sizes are beyone the 1k UTF-16 Codepoints limit.

Closes #3596
Improved logic that removes top-level folder from archives when needed

Whether we remove the top-level folder from the archive depends now on the zip itself and not on where it was downloaded from. That makes it work installing local files too.

Closes #3582
Replaced localhost with 127.0.0.1 in PluginManagerTests
test for primary allocating over replicas
still marked as await fix, requires investigation
Added errorStream null check in HttpClient (used for testing purpose)
Switched PluginManagerTests to use default plugins location and added check that http connector is working properly