more mysql errno support

[bbeaudreault]

@sougou we got a few more unbucketed errors in the last couple days so i went through and added a bunch more. This still isn't everything, but are the ones that looked obvious-ish.

[bbeaudreault]

@sougou if you don't mind, I just changed the "disallowed outside transaction" error to Code_FAILED_PRECONDITION instead of Code_INVALID_ARGUMENT. I think the former makes more sense here, according to the docs:

// FAILED_PRECONDITION indicates operation was rejected because the
	// system is not in a state required for the operation's execution.
	// For example, directory to be deleted may be non-empty, an rmdir
	// operation is applied to a non-directory, etc.
	//
	// A litmus test that may help a service implementor in deciding
	// between FAILED_PRECONDITION, ABORTED, and UNAVAILABLE:
	//  (a) Use UNAVAILABLE if the client can retry just the failing call.
	//  (b) Use ABORTED if the client should retry at a higher-level
	//      (e.g., restarting a read-modify-write sequence).
	//  (c) Use FAILED_PRECONDITION if the client should not retry until
	//      the system state has been explicitly fixed.  E.g., if an "rmdir"
	//      fails because the directory is non-empty, FAILED_PRECONDITION
	//      should be returned since the client should not retry unless
	//      they have first fixed up the directory by deleting files from it.
	//  (d) Use FAILED_PRECONDITION if the client performs conditional
	//      REST Get/Update/Delete on a resource and the resource on the
	//      server does not match the condition. E.g., conflicting
	//      read-modify-write on the same resource.

[sougou]

Looks like endtoend test needs fixing.

PS: If I wait long enough, maybe you'll finish this project for me :)

[sougou]

LGTM