use throwable in transport layer
catch throwable when processing messages in the transport layer, to report back failures even under errors
upgrade to mvel 2.1.5
update to joda 2.2
resolved empty setting values should be removed
when resolving empty settings values, their value should be removed, for example, when using ${env.ENV_VAR}, and ENV_VAR is not set, then the setting should be removed
Improved the stability of hl tests by adding waiting for at least yellow status.
In some test cases this was missing.
Made all the queries support `score_mode` parameter name in addition to the existing parameter name for score mode.
Closes #3026
Also support `sum` as `score_mode` option for the nested query.
Relates to #3026
Fix for RPM postinstall on old OpenSUSE distributions

Older OpenSUSE distributions do not ship with systemd and therefore are
using chkconfig, but do not have their scripts placed at /etc/init.d/
This patch is more defensive and adds additional checks in the postinstall
script to prevent aborted post install scripts, which makes the RPM
uninstallable.
Reduce branches in TopChildrenQuery

The branches used in the score method can be moved into the
scorer call and be essentially a constant operation rather than
a linear operation depending on the number of parent docs.
Ensure tests pass if store dir is a soft-link
Renaming span_multi_term query to span_multi

... due to discussing this on #2610 in order to have a more concise name
Not load the ids of child documents into memory.
Closes #3028
Expose LimitTokenCountFilter as a TokenFilter

Closes #3013
Added test for LimitTokenCountFilterFactory
Allow to disable allocation on the index level
Similar to the global cluster wide disable allocation flags, allow to set those on a specific index by updating its settings. The keys are the same as the cluster one, except they start with an index, for example: index.routing.allocation.disable_allocation set to true.
closes #3031
Make sure only relevant documents are evaluated in the second round lookup phase.

Both has_parent and has_child filters are internally executed in two rounds. In the second round all documents are evaluated whilst only specific documents need to be checked. In the has_child case only documents belonging to a specific parent type need to be checked and in the has_parent case only child documents need to be checked.

Closes #3034
Support for term facets on unmapped fields

Added support for unmapped & partially mapped fields (partially mapped fields may occur when searching across multiple indices where the faceted field is mapped on some and unmapped on others). If a shard doesn't have mappings for a field, the matching documents count on that shard will be added to the missing count for that facet.