Fix remaining leaked SearchResponse issues in :server:integTests

[original-brownbear]

This should be the last round for this module, found these using a prototype that has SearchResponse ref-counted already.

Tried to keep it as simple as possible, using assertResponse where possible. When it wasn't reasonable to use it or otherwise not the best option:

• try-finally in case variables got assigned
• shortened lots of hit-count assertions
• used dec-ref before reassigning variables in a couple tests that reused the same var for the search response in a loop, not the nicest but definitely the easiest to review option

[elasticsearchmachine]

Pinging @elastic/es-search (Team:Search)

[iverase]

LGTM