[SPARK-19155][ML] Make family case insensitive in GLM

## What changes were proposed in this pull request?
This is a supplement to PR #16516 which did not make the value from `getFamily` case insensitive. Current tests of poisson/binomial glm with weight fail when specifying 'Poisson' or 'Binomial', because the calculation of `dispersion` and `pValue` checks the value of family retrieved from `getFamily`
```
model.getFamily == Binomial.name || model.getFamily == Poisson.name
```

## How was this patch tested?
Update existing tests for 'Poisson' and 'Binomial'.

yanboliang felixcheung imatiach-msft

Author: actuaryzhang <actuaryzhang10@gmail.com>

Closes #16675 from actuaryzhang/family.

(cherry picked from commit f067acef)
Signed-off-by: Yanbo Liang <ybliang8@gmail.com>

mllib/src/main/scala/org/apache/spark/ml/regression/GeneralizedLinearRegression.scala

@@ -1027,7 +1027,8 @@ class GeneralizedLinearRegressionSummary private[regression] (
    */
   @Since("2.0.0")
   lazy val dispersion: Double = if (
-    model.getFamily == Binomial.name || model.getFamily == Poisson.name) {
+    model.getFamily.toLowerCase == Binomial.name ||
+      model.getFamily.toLowerCase == Poisson.name) {
     1.0
   } else {
     val rss = pearsonResiduals.agg(sum(pow(col("pearsonResiduals"), 2.0))).first().getDouble(0)
@@ -1130,7 +1131,8 @@ class GeneralizedLinearRegressionTrainingSummary private[regression] (
   @Since("2.0.0")
   lazy val pValues: Array[Double] = {
     if (isNormalSolver) {
-      if (model.getFamily == Binomial.name || model.getFamily == Poisson.name) {
+      if (model.getFamily.toLowerCase == Binomial.name ||
+        model.getFamily.toLowerCase == Poisson.name) {
         tValues.map { x => 2.0 * (1.0 - dist.Gaussian(0.0, 1.0).cdf(math.abs(x))) }
       } else {
         tValues.map { x =>

mllib/src/test/scala/org/apache/spark/ml/regression/GeneralizedLinearRegressionSuite.scala

@@ -757,7 +757,7 @@ class GeneralizedLinearRegressionSuite
        0.5554219 -0.4034267  0.6567520 -0.2611382
      */
     val trainer = new GeneralizedLinearRegression()
-      .setFamily("binomial")
+      .setFamily("Binomial")
       .setWeightCol("weight")
       .setFitIntercept(false)
 
@@ -874,7 +874,7 @@ class GeneralizedLinearRegressionSuite
        -0.4378554  0.2189277  0.1459518 -0.1094638
      */
     val trainer = new GeneralizedLinearRegression()
-      .setFamily("poisson")
+      .setFamily("Poisson")
       .setWeightCol("weight")
       .setFitIntercept(true)