Add better messages for read preference errors

Drivers should return useful error messages, as in the following examples, when there are no members matching the ReadPreference:

"PRIMARY cannot be combined with tags"
"No replica set primary available for query with ReadPreference PRIMARY"
"No replica set secondary available for query with ReadPreference SECONDARY"
For NEAREST, PRIMARY_PREFERRED, or SECONDARY_PREFERRED, "No replica set members available for query"
"No replica set member available for query with ReadPreference " + pref + " and tags " + tags