[SPARK-15183][Streaming] Adding outputMode to structure Streaming Experimental Api

[agsachin]

What changes were proposed in this pull request?

while experimenting with structure streaming. I found that mode() is used for non-continuous queries while outputMode() is used for continuous queries.
ouputMode is not defined, so I have written the some raw implementation and test cases just to make sure the streaming app works

Note:-
/** Start a query */
private[sql] def startQuery(
name: String,
checkpointLocation: String,
df: DataFrame,
sink: Sink,
trigger: Trigger = ProcessingTime(0),
triggerClock: Clock = new SystemClock(),
outputMode: OutputMode = Append): ContinuousQuery = {
As per me outputMode should be defined before triggerClock, the constructor with outputMode defined will be used more often then triggerClock.
I have added triggerClock() method also

How was this patch tested?

using unit test locally

(If this patch involves UI changes, please attach a screenshot; otherwise, remove this)

[AmplabJenkins]

Can one of the admins verify this patch?

[HyukjinKwon]

(I think it will throws an error for style check and should be as below:)

import org.apache.spark.sql.catalyst.analysis.{Append, OutputMode, Update, UnresolvedRelation}

[agsachin]

thanks I have fixed the scala style issues

[agsachin]

@tdas , @marmbrus any inputs on this.

[marmbrus]

Trigger clock is an internal details for testing that should not be exposed to users. Also, this isn't really what the output mode is for. Try reading the design doc posted on JIRA: https://issues.apache.org/jira/browse/SPARK-8360