Test: fix test to optimize and flush in the end to try to prevent 'Delete Index failed - not acked'
Completion Suggester: Fix CompletionFieldMapper to correctly parse weight
 - Allows weight to be defined as a string representation of a positive integer

closes #8090
[TEST] initialize SUITE | GLOBAL scope cluster in a private random context

Today any call to the current randomized context modifies the random
sequence such that cluster initialization is context dependent. If due
to an error for instance a static util method is used like `randomLong`
inside the TestCluster instead of the provided Random instance all
reproducibility guarantees are gone. This commit adds a safe mechanism
to initialize these clusters even if a static helper is used. All none
test scope clusters are now initialized in a private randomized context.