bug fix: SHARE and MODE are not keywords

Looks like share and mode are valid column names even though
LOCK IN SHARE MODE is a special construct. So, we can't treat
SHARE and MODE as keywords. Otherwise, the parser fails for
columns with such names.
queryservice: categorize read-only errors as RETRY

When we get a read-only error, it means that the current
server is not the master anymore. Categorize such errors
as RETRY, which will make the clients re-resolve to the
new master.