Refactor term analysis for simple_query_string prefix queries

Also fixes an issue where the token stream could be non-closed if an
exception occured.
[TEST] Disable compression in BWC test for version < 1.3.2

The compression bug fixed in #7210 can still strike us since we are
running BWC test against these version. This commit disables compression
forcefully if the compatibility version is < 1.3.2 to prevent debugging
already known issues.
Docs: note about confusing disk threshold settings