[TEST] Added ability to skip REST test suite/sections based on their required features

As we have different runners for the REST tests we need a mechanism that allows us to add features to any of them without breaking all others builds.
The idea is to name a feature and temporarily use skip sections that mention the required new features, so that runners that don't support it will skip the test.

Added support for `features` field in skip section.
Added `Features` class that contains a static list of the features supported by the runner. If a feature mentioned in a skip section is not listed here, the test will be skipped.
[TEST] clarified skip features usage
Add explanations for all AllocationDeciders

Relates to #4380
Relates to #2483
Remove support for boost in copy_to field

Currently, boosting on `copy_to` is misleading and does not work as originally specified in #4520. Instead of boosting just the terms from the origin field, it boosts the whole destination field.  If two fields copy_to a third field, one with a boost of 2 and another with a boost of 3, all the terms in the third field end up with a boost of 6.  This was not the intention.

  The alternative: to store the boost in a payload for every term, results in poor performance and inflexibility. Instead, users should either (1) query the common field AND the field that requires boosting, or (2) the multi_match query will soon be able to perform term-centric cross-field matching that will allow per-field boosting at query time (coming in 1.1).
Don't load CompetionTerms if lookupFactory is null

Closes #4970
Closes #4788
Prevent usage of object based RamUsageEstimator in Completion090PostingsFormat
Add RamUsageEstimator#sizeOf(Object) to forbidden APIs

This method can be a performance trap since it traverse the
entire object tree that is referenced by the provided object.
See LUCENE-5373
Added `fields` support to `geo_point` and `completion` field type.

Upgrading 0.90.x `multi_field` type that has a `geo_point` or `completion` field type as default field would otherwise fail.
Also it make sense to support these field types, because both support specifying the actual values as string.
Parent / child queries should work with non-default similarities
[TEST] Added check that yaml REST test suites always end with \n

Our yaml parser seems to be too tolerant in some cases, e.g. it properly parses yaml suites when they don't end with a line feed, whereas other clients tests break due to that. We should try to do the same to keep consistency across runners.
[TEST] Added ability to test apis that don't return json

The last response body gets now always stashed in the REST tests and can be retrieved via `$body`. This implies that not only expected values can be retrieved from the stashed values, but actual values as well.

Added support for regular expressions to `match` assertion, using `Pattern.COMMENTS` flag for better readability through new custom hamcrest matcher (adopted in do section as well). Functionality added through new feature called `regex` that needs to be mentioned in the skip sections whenever needed till all the runners support it.

Added also example tests for cat count api
Added dedicated test for MultiMatchQuery
Added exception if passed an invalid type param
Closes #4964
Added tests for match/multimatch queries with invalid “type” JSON param
Remove the in memory buffer Lucene store/directory
closes #4994
fix docs to reflect removal of byte buffer memory
Add [0.90.11] version as a constant
[TEST] fixed typo s/mising/missing
[TEST] added missing put warmer body
[TEST] added ability to filter REST test sections to run

Added `tests.rest.section` parameter that allows to filter the test sections that get executed via regex (case insensitive)