[query] Update Graphite find calls to complete unterminated queries with all possible path values for **

[robskillington]

What this PR does / why we need it:

Previously find calls did not special case ** and such were looking for terminated and unterminated queries for fields that had any value for the first graphite path index (since matchers created for ** are special and regex against the whole timeseries ID, they cannot be treated this way and need to complete all values for all possible path indexes).

This special cases the ** case and completes tag values for all of the path indexes that could be possibly relevant to the find query.

Special notes for your reviewer:

Does this PR introduce a user-facing and/or backwards incompatible change?:

NONE

Does this PR require updating code package or user-facing documentation?:

NONE

[linasm]

Don't have much of a context for this code, but one part of the implementation looks somewhat suspicious (see the comments inline),.

[wesleyk]

LGTM