[docdb] Restart read at global limit

[frozenspider]

Jira Link: DB-1544
After several attempts to restart read at current HT, we want to do a next restart at global limit time - thus eliminating the possibility of another "read restart" error.

Heuristics we discussed was switching to global limit when current HT is greater than start time + max clock skew (thus greater than global limit itself) - min(curr_ht, global_limit)

We might also specify a max number of restarts before we switch to global limit anyway